This suction lock has been designed to be used with silicone toys and allow them to be attached to items with a hole with a M8 threaded hole. E.g. a rod 

Sizing:

Large is designed for approximately 12.5mm diameter hole in Silicone toys

Small is designed for approximately 7-5.5mm diameter hole in Silicone toys.

Softer toys will generally have a smaller hole as the silicone has a higher elasticity and there for needs the smaller size hole to hold on to the lock.

Metal rod in photos not included