This is the multi-stepped crankcase bolt that is drilled through it centre to feed oil to the back of the crankcase wall, as well as providing a means to meter the feed of oil to the cambox, (in conjunction with item A11/41 , sold seperately).
This item is CNC machined out of Stainless Steel, it being copied exactly from an original bolt. As you can see - the bolt is cross drilled for the oilways in various places, as well as internally threaded for the adjuster bolt - which reflects in the price
Note: there have been slight variations in crankcase designs over the years. This part should fit most International and SOHC Manx type crankcases, but very early crankcases did have a smaller diameter on the bore closest to the lipped nut (the bolt can have its shoulder turned down to fit though). This type of early crankcase did not have such a pronounced counterbore at the back of the crankcase either, so length of this bolt may be nominal for that very early crankcase. If you are not sure, then email me for details of ours first, and we can confirm.