The bolt pattern on this swivel base will fit our downriggers and thumbscrew mounts (also compatible with Big Jon downriggers/thumbscrew mounts). It indexes every 22 ½° (16 positions) and engagement is held by a tapered stainless steel pin into a tapered hole to ensure that there is never any “slop” for the lifetime of this product. For ease of movement stainless ball bearing are installed on the top and bottom of the indexing wheel. The solid T-Handle assures easy grip when rotating the unit.