The threaded plugs have an external diameter matching the screw-in holes for DIN 3852 pipe bolt connections. The seal is embedded in a radial recess on the plane side, which makes the seal captive, so it cannot be squeezed out during tightening. The seal is also relatively soft, enhancing the sealing effect even on uneven surfaces. The finger grip allows for easy turning.
To see our entire line of fluid level indicators and related components, visit Section 12 of our online catalog.