Modern pin tumbler construction was developed in the mid 1800s and the bottom pin, driver and spring design has changed little in the last 150 years. One of the weaknesses of the pin tumbler lock is that it has to be fully disassembled in order to change the combination. Some companies have...
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The most popular system is A2. There are two shearlines, one for all operating key functions which is located at the plug shearline. The control sleeve forms a second shearline which is used by the control key. The dimension between the plug shearline and the control sleeve shearline is .125”. The A2 system uses depth increments of .0125”. Therefore a distance of 10 increments (10 X .0125 = .125) is formed between the two shearlines. There are a few exceptions depending on the cylinder usage, but the total .0125 increments of the bottom, master, control and top pins in an IC core cylinder (pin stack) usually adds up to 23.
Pinning example: Master key cut = 4, Change key cut = 8, Control key cut = 6.
Bottom pin = 4 (highest operating key cut / shortest bottom pin)
Master pin = 4 (4 + 4 = 8 / deepest operating key cut)
Add ‘10’ length to Control key cut (6 + 10 = 16 / added pin length for control sleeve shearline)
Chamber already has ‘8’ (4 + 4 = bottom & master pin total)
16 - 8 = 8 / Control pin length (bottom, master & control pin increment totals = 16)
Total in chamber = 4 + 4 + 8 = 16. 23 - 16 = 7 (top pin length needed to reach 23 total )
The A3 system uses depth increments of .018. Pin stacks equal 16. The A4 system uses increments of .021. Pin stacks equal 14. A3 and A4 systems were originally designed to allow development of large single-step master key systems but maximum adjacent cut rules prevented many key changes from being used. The result was that there was little advantage for using the A3 and A4 systems and the A2 master key system is generally used today in most cases.
Partial list of SFIC manufacturers past and present: Arrow, Best, CX5, Dom, Falcon, Kaba Peaks, KSP, Marks, Master, Medeco Keymark, Sargent, Schlage, Yale.
Each IC lock manufacturer has its own pinning system. For locksmiths who service many different types of IC systems, it can be difficult to remember which pinning system to use.