Pre-war knee pads

I am refurbishing the tank on my 1936 16H as what is left of some aged sealant in the rusty inside is breaking up and the whole thing needs sorting. Although externally the tank looks reasonable the bike came to me fitted with John Bull no.25 "pneumatic" knee grips as shown on the photo below. These are fitted to steel plates to give a screwless appearance and, because they are a different shape and longer than the correct Norton pads, a previous owner has redesigned the tank striping and logo position to suit these pads - well, sort of !

Having removed the John Bull pads and fitting plates I see there is a circular protrusion on each side of the tank of about 1?" diameter and about 3/16" deep, centered 2?" ahead of the screw holes. On one side the JB plate had been cutaway to fit around this protrusion. On the other side the centre of the protrusion has been fitted with a short threaded stud as an extra anchoring point for the JB plate.

These protrusions look like original fittings and because of the above must pre-date the fitting of the present JB knee pads. However I can't see what purpose they fulfil; indeed they would foul the fitting of Norton pads as they align with the front lip. The tank otherwise seems original matching the number on the factory record.

Before I remove these protrusions to fit Norton pads could anyone kindly suggest what they may be for.

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