When I redo a bike, I do my best NOT to use any of the OEM fasteners. I only use the "special" fasteners that I can't find otherwise. I buy stainless fasteners from Maryland Metrics
www.mdmetric.com which is also where I buy all the fasteners for my business. The reason I use them is that they have the largest inventory in the US of metric stuff. Unfortunately, their website is cumbersome to use so I call and speak to a fellow name Scott, one of their salesmen. He usually has to check for availablility and gets back to me in a day or two.
Anyway, MOST of the bolts on a Japanese bike are ISO standard and the screws are JIS standard. The bolts / nuts have been explained. A bolt, measured 6x20 is 6mm diameter and 20mm long. Most 6mm bolts on a Kawasaki use standard thread pitch which for a 6mm bolt is 1.00. There are a FEW fasteners used on the carburetors which use 0.75 pitch which is somewhat finer pitch. The finer pitch is generally used where there is an adjustment and the finer pitch allows a finer adjustment. An example is the idle stop screw.
Keep in mind that the nuts and bolts on a Kawasaki or any other application are measured by either the diameter of the bolt or the diameter of the hole in the nut which corresponds to the bolt/stud that goes in the hole. A 6mm bolt will require a 10mm socket to turn it.
Most of the thread pitch is pretty standard stuff up to a point. 4mm bolts (fasteners) will use .7 pitch, 5mm .8 pitch, 6mm 1.0 pitch, 8mm will use 1.25 pitch and MOST of the bolts sized over 8mm such as 10mm and 12mm (these make up MOST of the bolt sizes) will also use 1.25 pitch which is a bit unusual for metric applications. The shock studs are an example... these are 1.25 pitch as I recall which is pretty fine thread for that size stud. Not sure if this is a Kaw "feature" or standard practice.
Some fasteners on a Kaw are unusual and made specially for the application. The countershaft sprocket nut is an example. If memory serves it is a 20mm nut with 1.5 pitch. The odd thing is the outside size of the nut which requires a 27mm socket to remove. The STANDARD outside size for this size nut is 30mm. A 30MM nut CAN be substituted but most are too thick. Maryland Metric does sell a thin nut with 30mm outside width that works fine although there isn't much bend-over area on the lockwasher. I buy these instead of using old chewed up stock nuts.
I also buy assortments of stainless fasteners in most 6mm and 8mm sizes (assortment of lengths). If you decide to buy steel fasteners these are actually stronger but tend to rust. I buy mostly all socket head type. If you do buy steel, make sure they are zinc plated and not the "black" finish which will rust before you even turn your back on the bike.
The stainless socket head kits that Z1 sells actually are less expensive than purchasing the bolts separately from Maryland Metrics. When I did my last project bike, I DID buy all new stainless fasteners for the chassis. I had measured all the bolt lengths for the engine bolts and when I compared the prices, the z1enterprises kit that they sell came out to less so I just bought their kit and the additional chassis fasteners. The kits they sell are real well thought out and actually contain all the correct bolts where some of the ones sold on eBay DO NOT.
