Wheel bolt length

Does any one know the length of standard wheel bolts? My mot centre is questioning the thread engagement. I counted 6 turns which seems ok to me I'm pretty sure they're standard. The wheels are standard.

Also, are the heads 17 or 19 a/f?

Heads are 19mm. I think 6 turns is about right - doesn't seem a lot. Bolts are 52mm end-to-end.

Thanks guys. I'll let the garage know.