Any idea where to obtain such an item? I currently have a taper version, but of course this seals with PTFE and has to be done up tight. It's for blanking off a "rodding eye" on a seawater intake system, so I might potentially need to remove and refit it under awkward conditions and something with a fibre washer or O ring would be easier. The additional projecting length of the taper plug is also marginal whether it will fit inside the surrounding woodwork, so a shape like this would be good:
BES don't appear to have anything suitable.
Cheers,
Pete