These mount onto the front side of bass drums and are used to anchor the drum , and decrease sliding forward when being played. these require a single 5/8in dia hole for mounting. Pull out rod diamter is about 3/8in or 9.5mm. The posts measure 8 1/2 inches from tip to tip. These vintage style, pull out spurs are similar to the ones used by Gretsch or Ludwig on Club Date kits in the 60s.