Caster mounting styles consist of what are known as “Plate casters” and “Stem casters”. Plate casters comprise a flat square plate with holes at each corner, which are meant to align with the mounting pattern found on carts and fixtures. These holes form what is known as the “bolt hole spacing” or BHS and is critical in mounting the caster to any cart. These plates come in various styles and are meant for mounting to various objects, so it is important to ensure the bolt hole spacing on the caster is the same as the product it is being attached to. Occasionally, plate casters may be welded to the cart. In this case, no bolt holes are necessary and only the overall dimensions of the plate come into play.
On the other hand, stem casters use a single rod or stem protruding from the center line of the raceway to secure the caster to various objects. While plate casters are typically used for most medium and heavy duty applications, most common stem casters are for light duty applications such as furniture and medical equipment. Stem casters can be mounted using a variety of methods. These methods range from threaded rods of all sizes that screw in to hollow kingpin casters that slide over a stud and are bolted in place, to press-fit stems that snap into place securing the caster and cart together.
Displayed in the above picture are a stem caster (left), and a plate caster (right).