Law Enforcement Guide to Master Lock PDF

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Law Enforcements Code Book For The master Lock Combination PDF Free Download

Law Enforcement Guide

Probably the most common combination padlock used today is the Master Lock combination

Master Lock combination padlocks are typically found securing lockers, bicycles, and gates and are used in many other security applications.

Harry E. Soref, a locksmith and inventor, and James Keith Marshall were awarded a patent for
the Master Lock combination padlock on April 30, 1935.

The Master Lock combination padlock has a pressed steel case, which is press fitted and spun
over the back cover, making it impractical to disassemble the lock.

The padlock has three pre-set combination wheels.

The combination for a Master Lock combination padlock may be identified by looking up the serial number, located on the back of the padlock, in this code book.

The serial number on the padlock below is 903744 and the matching combination is 26-08-22.

To designate the series, serial numbers may start or end with a letter.

However, a Master Lock combination padlock may not include the letter as part of its serial number.

To open the padlock, rotate the dial right two or more turns, stopping at the first number.

Next, rotate the dial left one complete turn past the first number, stopping at the second number. Then, turn right to the third number and pull the shackle open.

The remaining pages in this book list Master Lock combination padlock serial numbers on the left side of the column with their corresponding combinations on the right.

Pictured below is an A-series Master Lock combination “Champ” padlock – model

Instead of “Master” the word “Champ” is stamped on the dial of some Aseries padlocks.

A-series padlocks have knurled dials to assist with turning.

Knurled dials are also used with V- and X-series padlocks.

The serial number for this padlock is A13825 with a matching combination of 30-04-30.

Two interesting points emerge when examining A-series serial numbers A30001- A39750.

The first point is that the combinations assigned to serial numbers A30001-A39750 are identical to the combinations assigned to serial numbers B30001-B39750 in the B-series.

The second point is that a repeating pattern exists in serial numbers A30001-A39750. The first serial number in this range “A30001” has an assigned combination of 38-04-22.

The same combination is assigned to the following serial numbers: A31537, A33073, A34609, A36145, A37681, and A39217.

The padlock’s combination is recycled after every 1,536th serial number.

If an individual had a Master Lock combination padlock with a serial number between A30001-A39750 and did not know the combination, they could add or subtract 1,536 from the serial number until a padlock’s serial number was found that could be associated with a known combination.

This also applies to B-series serial numbers B30001-B40752.


On the right is a picture of a Master Lock combination padlock with the back cover removed.

The shackle is the loop-shaped part of the padlock that does the fastening.

The bolt is the spring-loaded mechanism that engages the shackle.

The casing is the housing for the lock mechanism.

When the correct combination is dialed, the bolt is retracted from the shackle allowing the shackle to be pulled up and out of the casing.

A padlock shim is a triangular piece of thin flat metal or plastic capable of being inserted into a narrow or tight space in order to push back the padlock’s bolt.

Padlock shims come in a variety of sizes.

Most Master Lock combination padlocks are vulnerable to shimming.

However, manufacturing changes over the years have led to closer tolerances between the padlock’s case, shackle and bolt making shimming more difficult.

First, fully insert the tip of the shim along the side of the shackle as shown here.

Do not insert the padlock shim directly above the bolt.

This will result in damage to the shim If the tolerances between the shackle and casing are too tight, try pushing the shackle towards one side of the padlock to create a space for the shim.

Next, the shim is slowly turned 900 toward the bolt with the shim handles facing outward.

The shim may have to be worked back and forth in order to fully turn and retract the bolt.

With nothing securing the shackle, it may be pulled up and out of the casing.

Below are two close-up views of the bolt in the locked and unlocked positions.

Language English
No. of Pages2054
PDF Size10 MB

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