Security Pins: Spools, Mushrooms, and Pick Resistance

Definition

The Lock Industry Standards and Training (LIST) Council's Professional Locksmith Dictionary defines the common shapes:

• Spool pin: "a pin with a uniform smaller diameter except at its ends. Typically a top pin used to augment pick resistance but also observed as bottom and master pins."
• Mushroom pin: "a pin tumbler, usually a top pin, which resembles a mushroom. It is typically used to increase pick resistance."
• Dumbbell pin: "a spool pin with serrations at the larger diameter ends."
• Step pin: "a spool or mushroom pin which has had a portion of its end machined to a smaller diameter than the opposite end. It is typically used as a top pin to improve pick resistance by some manufacturers of high security cylinders."

The shared idea is shape. A cylindrical driver slides. A spool, mushroom, dumbbell, or step pin can hang up at the shear line and give false feedback. That is the defense. How an attacker responds to that feedback is outside this page.

Nineteenth-Century Origin

The idea of notching pins against picking is at least as old as Linus Yale Jr.'s US Patent 48,475, "Improvement in locks," granted June 27, 1865. The patent describes notched pin tumblers and notched containing recesses that "serve the purpose of… preventing to a certain extent picking of the lock." That is the conceptual ancestor of today's security pins: deliberately interrupted pin geometry that resists clean manipulation.

Place in High-Security Design

Security pins are one layer, not a whole lock. The LIST dictionary defines a high-security cylinder as one offering greater resistance to two or more of picking, impressioning, key duplication, drilling, or other forced entry. Sidebars, restricted keyways, and controlled blanks are other layers. See sidebar locks, restricted keyways, and high-security locks.

Similar ideas appear outside pin tumblers: false gates on disc detainers and combination wheels, and serrated levers. The principle is the same. Extra geometry creates false positions.

How Standards Write Them In

Standards treat security-pin features as evidence of pick resistance, under lab conditions.

• ANSI/BHMA A156.30 (High Security Cylinders). The 2014 edition includes, among its pick-resistance requirements, detainers "that have false notches, mushroom shapes or other constructions that impede manual picking." It also references UL 437's pick-resistance paragraph at some levels, and cautions that its tests "are performed under laboratory conditions" and that results in actual use vary with installation, maintenance, and environment. Pin and Ward is not stating which A156.30 letter level is highest until the current edition's text is checked.
• UL 437 (Key Locks). A 2007 DEF CON presentation by Marc Weber Tobias and Matt Fiddler summarizes UL 437 as including timed covert-entry tests for picking and impressioning.
• ANSI/BHMA A156.5 (Auxiliary Locks). The 2014 edition advises that "where pick resistance and other higher security protections are required," specifiers consider locks meeting UL 437 or A156.30.
• EN 1303:2026 (Europe). The 2026 edition of the European cylinder standard adds "requirements and evaluation methods for manipulation."

A rating describes a defined test. It is not a guarantee of immunity.

Limits

Security pins raise the time and skill cost of manipulation. They do not make a lock unpickable. TOOOL's 2005 bumping paper put the general point this way: "The perfect lock does not exist." Specifiers who need higher resistance look at the whole cylinder (pins, sidebar, keyway, listing) and at the assembly around it. See bypass.

Related Topics

• Lockpicking
• Raking
• Key bumping
• Pin tumbler locks
• Sidebar locks
• High-security locks
• Linus Yale
• UL 437

Sources