Three vacuum caps and three nickel-plated music wire spring clamps are included. The Version 5 vac cap is the usual Viton-B tube with a barbed nylon plug, which is clamped in place by a Teflon FEP band. The spring clamp is the Happy Fingers type, having loops at the ends so you can squish them open with your bare fingers.
The strength holding the nylon plug exceeds the tensile strength of the Viton B tubing. These will take a backfire without shooting a plug out.