Article below is a part of the assembly process of the UHF duplexer – main article is HERE.
Drawing below shows a [AL100] – Teflon Grommet.
Main purpose of the part is to make keep the coupling loop connection to the N socket centralised in the hole. Also it looks cool 😛
Some tips – it probably is a bit a cowboy job, but I cut them to length using a blade knife and mill out the slot using a rotary tool – I do not have a proper router yet…