Rest buttons and rest pads are used to provide a surface to locate or support a component in a jig or fixture. They are usually made of low-carbon or stainless steel and heat-treated or case-hardened.
There are many different types of rest buttons and rest pads. Standard products have a press-fit shank or a socket-head screw cap. Rest buttons and rest pads with flat, radius, and serrated heads are also available. Heavy-duty rest pads and heavy-duty rest buttons have a large, durable contact surface to support heavy workpieces, or to serve as wear plates. By contrast, screw rest buttons and screw rest pads have a relatively small contact area and can be used as a workpiece support or jig foot. Other types of rest buttons and rest pads include riser pads and round adapters.
Rest buttons and rest pads are measured in metric units such as millimeters (mm), or in English units such as inches (in) or fractions of inches. Measurements have lettered designations such as A, B, C, and D. English-style rest buttons and rest pads usually have a nominal diameter of 3/16", 1/4", 3/8" 1/2", 5/8", or 3/4". For metric rest buttons and metric rest keys, nominal diameters include 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, and 50 mm.
When constant wear wears requires replacement, suppliers of rest buttons and rest pads may be able to provide components that are within .0005 (.013 mm) of their original location. If replacement is not problematic, suppliers may recommend the use of unground rest buttons and unground rest pads. Rest buttons and rest pads are often made of low-carbon steel and case hardened. Low-carbon steels contain up to 0.30% C. The largest category of this class of steel is flat-rolled products, usually in the cold-rolled and annealed condition. Case hardening or surface hardening is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy. Case hardening is usually done after rest buttons and rest pads have been formed into their final shape, but can also be done to increase the hardening element content of bars to be used in a pattern welding or similar process.