Aaaah! Nuts!!!

Having cut all of my threaded and round rods to length, and checking everything in the kit of parts, I started the build …

… and then I stopped!

Aaaaghhh! The supplied M8 nuts don’t fit my M8 threaded rods!

They look like they should be the right size, but they just won’t go onto the threaded rods. The packet they came in identifies them as “Bossard BN 40054”.

I tried to find the nuts on the manufacturer’s website but the product code doesn't seem to exist; the nearest I could find were BN 40079 https://eu.shop.bossard.com/ch/index.cfm?app_page=0:31001:30002:11670:1 which should be the correct thread (1.25 mm metric pitch).
Comparing the supplied nuts with some standard M8 nuts which DO fit the M8 threaded rods, you can see the supplied nuts are shallower, so I suspect they are actually lock-nuts (not standard nuts), and they may have a fine pitch metric thread (1.0 mm pitch) or possibly a SAE thread, instead of a standard pitch (1.25 mm) M8 thread. (I don't have any tools to actually measure the threads.)

(Supplied nuts on the left, standard M8 nuts on the right. If you look very closely at the supplied nuts, they are stamped "H" and "04" - but I don't know what these markings mean.)

I got my build going again by buying a bag of standard M8 nuts from my local hardware store, and I have contacted my kit supplier to alert him to the issue - I suspect the company which supplied the nuts to him has either mis-bagged them, or they could be cheap counterfeit Chinese items.

Moral of the story – if you are buying a metric kit from a USA-based supplier, get them to check the metric parts carefully – they may not know how to check the dimensions of the various metric components.