The SCHOEPS RG 88 is a double swivel described by the manufacturer as the double version of the RG 8 swivel. Its stated application is attaching the R2C KC double active extension tube to an STR support rod with a diameter of 12 mm.

The official order number is 161405, and the technical information specifies a grey finish. SCHOEPS lists the R2C KC tube and STR vertical support rod as recommended accessories. Before installation, check those references and the 12 mm rod diameter, since they are the components specified for the application described by the manufacturer.