These OMS Book Screws feature an extra long {7/8 in | 22 mm) bolt; the shoulder on the nut will fit the usual 3/8-inch holes on metal backplates Book Screws are primarily used to attach BC wings, single tank adapters (STA), accessories such as backpads and inflation systems to backplates, but also have a multitude of other diving applications. The extra length is often necessary when there is a stack of three grommets to be secured such as occurs when attaching the OMS Soft Stabilizing Adapter, Wing, and IQ pack to a backplate. Made from stainless steel and sold individually, .