The Hollow extension is presented by Doc Johnson (maker), Mainman (advanced reviewer) and EdenFantasys

Securely strap on your nylon harness then attach any of a selection of dildoes. This harness has an adjustable waist up to 44", an open crotch for maximum comfort, easy access, and non-slip action, all designed to give you command and control for your erotic pleasures. The vac-u-Lock plugs attach with velcro or snaps. Includes hollow extension to insert your penis. This device is compatible with all vac-U-Lock attachments. 7" long, 1 3/4" wide, 5 1/2" around.