Would anyone know the kickstart pinch bolt size. part number 000367, no size given.
I take it you want to fit the best bolt you can and not the 8mm bolt from B&Q.
If you have the kickstart you should be able to draw the bolt and give the drawing to an engineering company. (If you can't find the proper part.)
You need to measure the diameter of the hole that the bolt enters. The side of entry for the bolt is from the top of the kickstart when the lever is halfway through it's stroke and roughly horizontal.
From memory this is 5/16 ins and can be checked if you have a 5/16 ins drill shank.
Now measure the length of clamp on the kickstart. From where the bolt head will sit to the where the nut and washer will sit.
Subtract 1/8 ins and this is the length of unthreaded portion of the bolt.
Measure height of a 5/16 cycle nut from somewhere else on the bike. Probably 1/4 ins.
Total length of the bolt will be measured from under the head and will be kickstart clamp length, plus nut, plus 2mm for a plain and spring washer plus, plus 1/8 ins for thread poking out of nut. Mine is just under 1.5 ins long.
The head at the top of the bolt is a full size. 1/4 inWhit is the ID on the spanner jaws.
The nut is a reduced size. 3/16 inWhit on the spanner jaws.
The unthreaded portion gives extra strength. The unthreaded portion is essential to stop the kickstart coming off the splines. It should be impossible for the kickstart to come off the splines if the bolt is fitted loose or tight.
The thread is 5/16 BSC.
The different hexagon sizes are to allow tightening with the standard spanners carried in a toolkit where it is assumed you will have one spanner of each size, but probably not two of the same size.
If you look at other threads related to lightweight kickstarts you will see the splines in a kickstart lever need all the support they can get.
Why two washers under the nut?
This would seem to me to be counterproductive.
The lockwasher would turn with the nut and not be "locked" to the casting.