My plastic arch liner didn't have a hole, or any outline
of one, to gain access to the crank nut which is useful when checking valve clearances etc.
I bored a 70mm hole in order to fit the socket I have, then realised that size grommet
is not a typical dimension!
I found a rubber one in China eventually, took a month to arrive, hey ho.
Not particularly good quality, rather thin, but did the job.
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