It is a multifunction adapter rod clamp / rail block. It can be used to assemble a simple tripod plate, single front handle or a lens support. (Please note: the 1/4"UNC mounting hole is not a through hole.)
For 15mm rod support / rail system. Specially for DIYers and EOS movie makers
It can extend application of rod support rail system.If you have more gears, the rods clamp is helpful.