Vac U Lock — Knuckle Up by Doc Johnson

Vac U Lock User Guide & Play Styles

Hands-on technique: getting the most from this strap-on harness system

The Knuckle Up is designed for couples who already understand how a strap-on harness works and want direct tactile control beyond what a conventional harness delivers. Slide your fingers through the one-size knuckle rings, seat a chosen attachment onto the vac u lock plug, and you control depth, angle, and rhythm entirely by hand — making it one of the best strap on harnesses accessories for technique-driven partnered play. The phthalate-free black body stays comfortable in extended sessions. After play, wipe down with a dedicated toy cleaner to keep the interface clean for the next attachment swap. For deeper context on building out your shared toy kit, explore our Couples Pleasure pillar guide or browse the full harness-only range.