ProMaster's Long Lens Plate is used to balance long lenses and heavy or awkward camera rigs on gimbal heads, ball heads, and cine/video heads. The extra length of this plate allows it to slide back and forth in a dovetail head (arca-type) until the proper balance point is found. Then it is locked in place for the best stability when using movements on the head.
This long lens plate can also be used as an anti-twist remedy for lenses and cameras that have two threaded connection ports on their bottom side. The plate includes both a 1/4"-20 and 3/8"-16 connection bolt. Many long lenses have two tripod ports, with each being one of these sizes. By connection both bolts to your lens or camera you will drastically improve stability and eliminate any possible twisting of the lens or camera on the plate.
The connection bolts are both removable from the plate if no needed. They can also be used in other slots on the plated, especially the 1/4"-20 bolt which fits into every slot. Finally, two small safety bolts are located at either end of the Q/R plate to prevent it from accidentally slipping off a head when it is not locked down. These safety bolts can be removed if you so choose but be extra careful not to allow your rig to slide out of the head and fall.