There are many types of guitar strap locks, but they all serve a common purpose. Strap locks work as a barrier between the strap and the outside of the guitar's strap button to prevent accidental disconnection of the strap from the guitar. Some guitar strap locks are designed to be installed on the strap and require minor guitar modification, while others are stand-alone units which can be fitted without alteration of the strap or guitar.
Metal Washer Strap Locks
The simplest type of strap lock is the washer type. Found in hardware stores, round metal washers are installed by unscrewing the strap button from the guitar. A washer of suitable size is placed over the narrow-tapered end of the strap button on the side that makes contact with the guitar, and the wide outside-tapered end of the strap button prevents the washer from slipping over the button. The strap is placed onto the narrow side of the button, and the button is screwed back on to the guitar. The strap is now sandwiched securely between the guitar body and the washer. Although effective, this design requires the strap remain installed on the guitar, as removal will require unscrewing the strap button.
Rubber Washer Strap Locks
Rubber washers used on plumbing fixtures and some beverage containers are an alternative to metal washers. Rubber washers of sufficient size are slipped over the outside of the strap button after the strap is installed, and can be removed or replaced without removing the strap button. The primary drawback of rubber washers is they may stretch over time and will require periodic replacement.
Clip-on Strap Locks
Plastic clip-on strap locks are inexpensive (under £6 as of June 2010) and readily available at music stores. They work on the same principle as washers by providing a barrier between the strap and the outside of the strap button, but are adjustable to fit most common strap button sizes. They slip over the strap and strap button, and are adjusted for a snug fit on the button by turning a small tightening mechanism.
Built-in Strap Locks
Some guitar straps are sold with a strap lock built-in to the strap holes. These straps are placed on the strap buttons in the traditional way, and use a plastic spring-clip mechanism to hold the strap securely onto the button. This type of strap and strap lock combination is only offered by certain manufacturers, limiting your choice of material and design.
Mechanical Strap Buttons
Mechanical strap buttons are the type used by many professional guitar players, and are sometimes provided as standard equipment on some high-end guitars. There are several designs, but all require minor guitar and strap modification. Mechanical locks consist of a special strap button and the strap-installed lock. The stock button on the guitar is removed and replaced with the supplied button and screw. The strap lock is placed in the strap holes and held in place by a washer and nut or metal spring-clip. The strap lock is inserted on the strap button and locked into place by a metal pin or spring ball-bearing system, and is removed by pressing or pulling a lever to disengage the lock. While somewhat expensive (starting at around £9, as of June 2010) plus installation time, they provide secure mechanical locking of the strap. These strap locks render the strap useless on standard strap buttons, and the special strap lock buttons are not suitable for use with a standard strap. Users of this type of strap locking system usually have them installed on all guitars used, making the strap compatible with more than one guitar.