Need some engineering advice (M6R Rack Skate Wheel - only one keeps coming off)
So I've replaced the EZ Wheels on my M6R with 76mm skate wheels, but for some reason one of the bolts keeps loosening and threatening to fall off.
I can't figure out why a single skate wheel has almost fallen off like 4-5 times while the other 3 wheels are still perfectly secure. All the bolts and nuts were purchased brand new - 2 x M5 and 2 x M6 - at the same place with the same specs. They were fixed with the same number of reused washers on both sides.
I'm sure there must be a perfectly common explanation for this somehow, yet I can't think of it. Any suggestions would be appreciated - especially if it doesn't require extra $ like buying Loctite.