Petcock

I bought one of these - 033155 from the NOC shop for my 1958 '99 as it looked just the same as the leaking one the bike came with - it fitted fine, seemed very reasonably priced. If you only have one tap then buy a 'Reserve' one as the 'Main' one doesn't let you get the last bit of fuel out.

Usually 1/4 BSP. into the tank,   ( which looks far bigger than 1/4  !! )   but thats the way it is.

made a two-slider tap which I believe is correct for the bike.  Two round sliders with cork on them to seal, opposite each other across the tap.  It's not that good as a tap, as the reserve gives 3.2 miles.  I have proved that.... twice so far.

If you can only get a 'Main' you can remove the filter mesh, cut down the metal tube and then refit the filter mesh so the tap effectively becomes a 'reserve' allowing more of the fuel to be used.