This black rubber t-style grommet is 16-17mm id and 19-20 od. The groove in the o-ring will fit holes about 17-19mm and allow a tube about 16mm in diameter to pass inside.
Item’s Dimensions:
Inner Diameter: 16-17mm Outer Diameter: 19-20mm
Item’s Recommended Uses:
This grommet is perfect for matching a tube inside another tube when the seal has a very little gap.