This has a NPT tapered thread

NOT ....BSP (19 T.P.I.).... as found in the custom MUSTANG tanks

Adapters are available for 57-74 & 75 up Harley tanks in our ebay shop

(( Or chase through with a NPT machine tool tap...as it is very...very close to that thread )) 

We have also found some tanks may need deeper thread taping out to acheive more than a couple of rotations in. I have a listing for our machined weld on bungs, which will use up around 3/4 of the thread length.

9/16" ( 13.5 mm ) outside diameter measured at the larger end of the taper 18 T.P.I. thread.

Not an alloy casting ( like those that kept shearing off ) but made from steel.

The square body measures approx 17mm with a 15mm thread length. 

The colour of the plating may vary from ones photographed  ( we shall match best for pairs purchased )

I have had these apart and they are well made, i only sell products that i would buy for my own personal use....Nic