Bottle Cap, Polypro, Two Piece, Has an outside screw ring and an internal center piece that the tubes go through. This design allows you to turn the ring to tighten or loosen the cap while allowing the tubes that go through the center piece to remain stationary. The center piece has holes to accommodate 3 ea 1/8 in OD tubes. This cap was originally designed and used on he Biosearch Model 8800 large scale oligo synthesizer.