CompX Locks Secure Apartment and Commercial Mailboxes

CompX National is the only authorized manufacturer of the USPS-L-1172C mailbox locks developed specifically for newer centralized mailcenters.


According to statistics collected by the Postal Inspection Service, mail theft is a growing problem nationwide. Mail security has become a major concern since identity theft is one of the reasons for mail theft.

In an effort to limit mail theft, the United States Postal Service (USPS) presented a proposal to increase the level of security for centralized mail receptacles. Within the 2004 proposal were recommendations for improving the level of security of the mailboxes and the lock. These recommendations included higher strength locks and to increase the number of key codes.

USPS specification USPS-L-1172C went into effect October 2006, requiring new mailbox locks to have a stainless steel plug that enables the lock to withstand 1,000 pounds of force applied to the cam. The previous specification, USPS-L-1172, required the plug to withstand only 100 pounds of force. Also required is a 3/16” heavy duty, stainless steel cam that provides additional security.

A total of 4,000 key codes are used by the new lock mechanism. The specification includes visual recognition of the new mailbox lock. To easily identify these locks, USPS-L-1172C is coined into the face of the lock housing.

For new construction or major renovation, multiple family dwellings or commercial office space must use the new 4C centralized mailbox receptacles manufactured by Auth-Florence. These centralized mail receptacles include the NDCBU (Neighborhood Delivery Collection Box Units) and CBU (Cluster Box Units).

To satisfy the lock requirements, the USPS contracted CompX National to domestically produce the new lock. CompX National introduced the C9100 and C9200 mailbox locks to satisfy U.S. Postal Service specification USPS-L-1172C. CompX National is the only authorized manufacturer of the USPS-L-1172C mailbox locks developed specifically for the 4C mailboxes.

These five pin tumbler mail box locks have five depths of cut (0-4).

Spacing Cut-to-cut .106”

  • 1- .150” 2- .256”
  • 3- 362” 4- .468”
  • 5- .574”

Depths Increment .018”

  • 0- .247” 1- .229”
  • 2- .211” 3- .193”
  • 4- .175”

Code Cards: 1200 CM C107, Universal II 1107

CompX National C9100 mailbox locks rotate 90 degrees clockwise while the C9200 mailbox locks operate 90 degrees counterclockwise. To achieve 4000 key codes, there are two keyways, or blanks, each containing 2000 codes. The key code series for the D4300 key are 1000-1999PS and 3000-3999PS.

The key code series for the D4301 key are 2000-2999PS and 4000-4999PS.

Aftermarket key blank numbers include:

  • National Original D4300: Ilco 1646, Jet D4300, JMA NTC-14D
  • National Original D4301: Ilco 1646R, Jet D4301, JMA NTC-14

The 4C mailboxes have a new smaller cutout designed specifically for the C9100/C9200 locks. The new cutout will not accommodate the Double “D” (earlier) cutout used by the pin tumbler-equipped mailbox locks.

According to the USPS-L-1172C specification, earlier mailbox locks cannot legally be used in the new 4C mail receptacles. The purpose of having the USPS-L-1172C coined into the face of the lock is to provide visual recognition for the mail carrier and anyone installing the lock. If the C9100/ C9200 lock is not installed into a 4C mail receptacle, the mail carrier should not leave mail in the mailbox.

National C9100/ C9200 mailbox locks are secured to the metal door using a spring clip. A second slot accommodates a thicker door installation. The stainless steel cam is held in place by a castle nut. CompX strongly recommends that while applying torque to the nut, the cam be prevented from rotating. The USPS approved cam, CompX part number C7120, is sold separately when purchasing replacement locks. Drain holes at the bottom of the lock housings help eliminate moisture.

For more information, contact your local locksmith distributor or CompX National, P.O. Box 200, Mauldin, SC 29662. Telephone: 864-297-6655. Web Site: www.compx.com/national.html.

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