You want a compact, weatherproof mailbox lock that resists tampering and fits common housings. Choose from Prime-Line U9940 (ILCO 1003M), MP4526 insert kits, a Universal MP4945-style lock, Prime-Line MP4573 (NA‑14), or the TIKSCIENCE heavy-duty 5‑pack for multiple units. Look for 5‑pin cylinders, nickel/zinc plating, and multiple cams for fit and durability. Each option balances security, corrosion resistance, and DIY-friendly installation—keep going to see specs, compatibility, and installation tips.
| Prime-Line U9940 Brass Mailbox Replacement Lock (ILCO) |
| Durable Classic | Keyed lock: 5-pin tumbler lock (2 keys included) | Includes keys or replaces keyed parts: Includes 2 keys | 90° rotation: Opens counter-clockwise, 90° rotation | VIEW LATEST PRICE | Read Our Analysis |
| MP4526 Mailbox Lock Replacement with 2 Keys |
| Best All-Rounder | Keyed lock: Combination/insert lock (2 NA-14 keys included) | Includes keys or replaces keyed parts: Includes 2 NA-14 keys | 90° rotation: Opens 90° clockwise | VIEW LATEST PRICE | Read Our Analysis |
| Universal Mailbox Lock with Keys (Fits MP4945) |
| Easy Universal Fit | Keyed lock: Cylinder lock (2 keys included) | Includes keys or replaces keyed parts: Includes 2 keys | 90° rotation: Counter-clockwise rotation (standard 90°) | VIEW LATEST PRICE | Read Our Analysis |
| Prime-Line MP4573 Nickel Mailbox Replacement Lock (NA-14) |
| Reliable Replacement | Keyed lock: Cylinder lock (NA-14 keyway; keys included) | Includes keys or replaces keyed parts: Includes keys (NA-14 keyway) | 90° rotation: Opens counter-clockwise with 90° rotation | VIEW LATEST PRICE | Read Our Analysis |
| TIKSCIENCE Heavy-Duty Mailbox Cam Lock 5-Pack |
| Heavy-Duty Pack | Keyed lock: Cam replacement set for cylinder locks (fits specific keyed models; used with keyed cylinders) | Includes keys or replaces keyed parts: Cam pack (replaces cams used by keyed mailbox locks; sold as parts for keyed systems) | 90° rotation: Cam profile designed for standard cylinder/cam 90° key turns | VIEW LATEST PRICE | Read Our Analysis |
More Details on Our Top Picks
Prime-Line U9940 Brass Mailbox Replacement Lock (ILCO)
Provided you need a straightforward, durable replacement that fits common mailbox brands, the Prime-Line U9940 is a solid choice—you’ll get an ILCO 1003M 5-pin tumbler lock that opens with a 90º counter-clockwise turn and comes with two keys and multiple zinc-plated cams to match several mailbox models. You’ll install a diecast body with a brass-plated face, brass pins, and a spring steel locking clip built for long-term use. Five zinc-plated steel cams let you adapt to American Device, Auth-Florence, Bommer, and Miami Carey boxes. Key-retention prevents removing the key when unlocked, helping guarantee you don’t leave it open.
- Keyed lock:5-pin tumbler lock (2 keys included)
- Includes keys or replaces keyed parts:Includes 2 keys
- 90° rotation:Opens counter-clockwise, 90° rotation
- Corrosion / weather resistance:Brass-plated face, durable materials (suitable for long-term use)
- Easy installation / replacement:Multipurpose replacement lock (simple replacement)
- Intended for mailboxes / mailbox compatibility:Compatible with American Device, Auth-Florence, Bommer, Miami Carey
- Additional Feature:ILCO 1003M keyway
- Additional Feature:Brass-plated face
- Additional Feature:Key-retention feature
MP4526 Mailbox Lock Replacement with 2 Keys
Provided you’re replacing a USPS or mailroom lock and want a quick, durable swap, the MP4526 is a smart pick — it fits popular brands like Auth‑Electric and Bommer, installs in under 10 minutes with universal mounting plates, and comes with two NA‑14 keys. You get a nickel‑plated metal insert lock with a 90° clockwise opening, five cams, and a key‑cannot‑be‑removed‑when‑unlocked feature that forces relocking. It’s scratch- and corrosion-resistant for outdoor use, resists prying, and ships as a single 1x1x1‑inch, 2.89‑ounce unit. Instructions, warranty info, and price‑match options are available on the retailer page.
- Keyed lock:Combination/insert lock (2 NA-14 keys included)
- Includes keys or replaces keyed parts:Includes 2 NA-14 keys
- 90° rotation:Opens 90° clockwise
- Corrosion / weather resistance:Nickel-plated, scratch- and corrosion-resistant, suitable for outdoor conditions
- Easy installation / replacement:Universal mounting plates and step-by-step instructions; replace in under 10 minutes
- Intended for mailboxes / mailbox compatibility:Compatible with Auth-Electric, Bommer, Cutler-Federal, Florence, Superior and several popular mailbox brands
- Additional Feature:NA-14 keyway
- Additional Feature:Clockwise 90° opening
- Additional Feature:Nickel-plated finish
Universal Mailbox Lock with Keys (Fits MP4945)
Should you want a straightforward, durable replacement that fits most standard mailboxes—including Prime-Line MP4945 models—you’ll appreciate this universal mailbox lock with two keys. You get nickel-plated, rust-resistant construction that withstands extreme temperatures, so it lasts. It installs in minutes with no complex tools or pro help, and uses counter-clockwise rotation. Five different lock specifications are included to match common housings, making it a flexible replacement option. By upgrading, you improve mailbox security and better protect letters and small packages. It’s a practical, low-effort way to restore function and safety to residential or commercial mailboxes.
- Keyed lock:Cylinder lock (2 keys included)
- Includes keys or replaces keyed parts:Includes 2 keys
- 90° rotation:Counter-clockwise rotation (standard 90°)
- Corrosion / weather resistance:Nickel-plated, rust-resistant, withstands extreme temperatures
- Easy installation / replacement:Easy installation in minutes; no professional help required
- Intended for mailboxes / mailbox compatibility:Fits most standard residential and commercial mailboxes; fits Prime-Line MP4945
- Additional Feature:Fits Prime-Line MP4945
- Additional Feature:Five lock specifications
- Additional Feature:Withstands extreme temperatures
Prime-Line MP4573 Nickel Mailbox Replacement Lock (NA-14)
Should you need a quick, reliable mailbox fix, the Prime-Line MP4573 (NA-14) is made for you — it’s a multipurpose replacement that fits most mailboxes and comes with five cams for easy compatibility. You’ll install a durable diecast lock with brass and stamped steel parts; steel components are zinc-plated and the cylinder face is nickel-plated for corrosion resistance. It opens counter-clockwise with a 90° rotation and uses the NA-14 keyway. The key can’t be removed when released, so you won’t forget to relock. The set includes a retaining hex nut and clip, making this an easy, practical replacement.
- Keyed lock:Cylinder lock (NA-14 keyway; keys included)
- Includes keys or replaces keyed parts:Includes keys (NA-14 keyway)
- 90° rotation:Opens counter-clockwise with 90° rotation
- Corrosion / weather resistance:Zinc-plated steel components, nickel-plated face (corrosion-resistant)
- Easy installation / replacement:Simple replacement installation; intended as easy fix
- Intended for mailboxes / mailbox compatibility:Multipurpose replacement for several mailbox brands; works with most mailboxes
- Additional Feature:Includes retaining hex nut
- Additional Feature:Zinc-plated steel parts
- Additional Feature:Counter-clockwise 90° rotation
TIKSCIENCE Heavy-Duty Mailbox Cam Lock 5-Pack
Should you need a rugged, budget-friendly replacement for multiple cluster or curbside mailboxes, the TIKSCIENCE Heavy-Duty Mailbox Cam Lock 5-pack delivers a hardened, precision-stamped steel cam that resists wear and tampering while keeping installation simple for DIYers. You’ll appreciate its precision-machined cam profile for smooth releasing and clear tactile feedback, plus multiple surface treatments that enhance weather resistance and long-term stability. It fits common standards (CompX C9100/C9200, Florence 1570F, USPS-L-1172C) and replaces C7120. At about 10.6 ounces per pack and easy to install without special tools, it’s a practical, cost-effective option for multi-unit maintenance.
- Keyed lock:Cam replacement set for cylinder locks (fits specific keyed models; used with keyed cylinders)
- Includes keys or replaces keyed parts:Cam pack (replaces cams used by keyed mailbox locks; sold as parts for keyed systems)
- 90° rotation:Cam profile designed for standard cylinder/cam 90° key turns
- Corrosion / weather resistance:Multiple surface treatments for wear resistance and anti-aging (high weather resistance)
- Easy installation / replacement:Easy installation design; no professional tools or complicated steps
- Intended for mailboxes / mailbox compatibility:Fits CompX National C9100/C9200, Florence 1570F, USPS-L-1172C CBU STD-4C; replaces C7120
- Additional Feature:Precision-machined cam
- Additional Feature:High-strength stamped steel
- Additional Feature:Five-pack replacement set
Factors to Consider When Choosing Mailbox Locks
At the time choosing a mailbox lock, you’ll want to check compatibility with your mailbox model and decide which lock type fits your security needs. Pay attention to keyway and rotation specs, plus the material and finish for durability. Don’t forget weather resistance ratings to make sure the lock holds up in your climate.
Compatibility With Mailbox
Start matching the lock with your mailbox’s mechanical and physical specs so it operates smoothly and fits securely. Verify the keyway type and cam orientation (e.g., 90° clockwise or counter-clockwise) so the replacement cylinder will physically move the latch. Confirm the number and shape of cams—many mailboxes use five—and that included cams align with the mailbox’s cam mounting and indexing. Check cylinder length, face diameter, and mounting hardware compatibility (nut/clip or retaining hex) so the lock sits flush and secures properly. Assure finish, material thickness, and corrosion resistance suit the mailbox’s exposure to prevent fit problems from rust or thermal expansion. Finally, match key-retention and rotation features to intended user behavior and mechanism operation.
Lock Type Selection
Because your mailbox is both exposed and frequently used, pick a lock that balances security, weather resistance, and mechanical fit. Decide whether you want a cam/insert keyed cylinder or a combination/digital unit—keyed locks give traditional control, while keyless options add convenience. Choose 5‑pin (or higher) tumbler cylinders for stronger pick resistance and more unique keying than wafer or two‑pin designs. Prioritize metal construction and corrosion‑resistant finishes so the mechanism survives rain, salt, and temperature swings. Make sure the lock’s cam and mounting style match your mailbox for straightforward installation. Finally, consider key‑retention features so the key can’t be removed while unsecured, reducing the chance you leave it unsecured after use.
Keyway And Rotation
Check the lock’s keyway and rotation specs before you buy or replace a mailbox cylinder, since the key profile, turning direction, and rotation angle all determine whether the cam will engage the latch correctly. You’ll want a replacement with the same keyway (NA-14, ILCO variants, etc.) so you don’t need new keys or a rekey. Confirm rotation direction—clockwise or counterclockwise—matches the cam and latch to avoid improper operation. Match rotation angle, typically 90°, to your latch travel so the cam fully engages without binding. Consider key-retention features should you need the key to stay in the locked position; they affect how and at what point the key can be removed. Verify keyway and rotation specs prior to installation.
Material And Finish
Choosing the right materials and finish for a mailbox lock keeps it functional and good-looking through years of weather and use. You should pick corrosion-resistant metals—stainless steel, brass, or zinc‑plated steel—for outdoor locks to prevent rust and maintain operation in wet or coastal areas. Brass pins and internal components give reliable tumbler performance thanks to corrosion resistance and machinability. Look for nickel or chrome plating for a hard, scratch‑resistant surface that preserves appearance. Powder-coated or plated faces and cams reduce oxidation and galling between moving parts, improving longevity and smoother action. Also consider thermal stability: metals with low expansion and high heat tolerance keep tolerances tight so the lock turns reliably in temperature extremes.
Weather Resistance Rating
At any time you’re picking a mailbox lock, prioritize its weather-resistance rating so the mechanism keeps working through rain, salt air, and temperature swings; look for corrosion‑resistant finishes or stainless components, sealed cylinders and cams, and specs that show wide operating temperatures to avoid moisture, freezing, or thermal binding. You should choose nickel-, zinc-, or chrome-plated locks or stainless-steel parts for coastal or humid sites. Check for sealed or weatherproofed cylinders and cams to keep out moisture, dirt, and insects. Verify temperature tolerance (for example, −40°F to 140°F / −40°C to 60°C) to prevent binding from expansion or contraction. Prefer UV-resistant coatings and polymers with gaskets, protective boots, or drainage paths that divert water and limit long-term corrosion.
Security Features Included
Why does the lock’s internal design matter to your mail’s safety? You want a multi-pin tumbler (commonly five pins) because more pins increase key variation and resist simple picking. Prefer key-retention so the key can’t be removed once released — that forces relocking and reduces accidental exposure. Check for corrosion- and weather-resistant finishes like nickel or zinc plating and durable metal cams to prevent outdoor failure. Inspect cam and clip construction: stamped or precision-machined steel cams with hardened clips stand up to prying and forced rotation. Finally, pick locks with a 90° rotation and matched cam profile so operation stays smooth while minimizing leverage points for forced entry. These features together make your mailbox far harder to compromise.
Ease Of Installation
Don’t let installation be the reason you avoid upgrading your mailbox lock: pick a cam-and-cylinder unit with included mounting hardware and clear instructions so you can usually swap it in under 10 minutes with just a screwdriver and wrench. You’ll want to confirm the rotation direction and degree—most are 90° clockwise or counterclockwise—so the cam aligns with your latch without modification. Measure door thickness and hole diameter to verify the replacement cylinder and retaining nut fit securely; that prevents drilling or enlarging holes. Prefer kits with multiple cam options and step-by-step guides to avoid trial-and-error and locksmith calls. Finally, check the package includes keys and small parts (cams, retaining clip or hex nut) so you don’t need extra purchases.
Maintenance And Durability
Because mailbox locks face constant exposure and repeated use, you should prioritize materials and upkeep that keep them operating reliably for years. Choose locks made from corrosion-resistant metals like stainless steel, brass, or zinc-plated steel to resist rust and outdoor degradation. Install weather seals or gaskets around the escutcheon and keep drainage holes clear to prevent water ingress and internal corrosion. Inspect the cylinder and cam annually and lubricate with a graphite or Teflon-based product to prevent binding and extend service life. Monitor key retention and rotation smoothness; increased torque, sticking, or failure to remove the key signal internal wear. At the initial sign of sloppy key action or excessive play, replace worn pins, springs, or cams to avoid sudden lock failure.
