Bolt length - is it an issue?

I have a problem. - while here in Australia I can get metric bolts by the tonne (that is a metric ton) (lol) (giggles hysterically as I type this), the actual lengths in the parts list at my local Bunnings and/or Masters(closing down) are not always present. the have lengths that might be 5mm under, or 5 to 10mm over what is listed in the parts list.

So my question to the community, is that bolts from the list have to be “exactly that long” due to things like clearance between parts, and what bolts can be a bit longer (i.e. clearance is not an issue).

Secondly, it is also not clear what bolts need what type of head i.e. HEX, philips, flat, or spanner and what type of form i.e. Flat, countersunk, round or button(yes they are 2 different things), since I think in some parts of the assembly (and ongoing support and maintenance) having the correct head for the bolt (you cant really have a different form factor for the nut) will impact who easily it gets put together and/or on-going support.

I understand that weight is always a consideration, but sourcing the metric bolts in exact lengths and quantities is a problem, and trying to find a single online shop that has them them all is like ----ing in the wind.

Hope you can help (I got motors/electronics/tubes[25mm]/bearings/print parts as I type).


It they are to long, put a normal nut on, take mister angry the anglegrinder, cut to size, take the burs of and take the but off to restored the threads.

The only ones that you need to be pretty close with are the 5/16x1.25", and really only 4 of those are critical so you could get out mr angry if you need to. The rest, longer is probably better than shorter.

As for the heads, as flat as possible (only a few where this matters so you could grind if needed) and no countersink heads.

I did what I could to make everything pretty universal, Most anything within reason should work. If you are using metric screws, some of the nut traps will not trap the nut, which is fine. Some will just need some glue (I use it on mine anyway) or some will need needle nose pliers. No big deal.

If you are using metric screws, some of the nut traps will not trap the nut,

Yeah found out about that.
Used a bit of 1mm cardboard to fill up the gap.