Hello Everyone
I am working through the final parts of my machine design and the more I go into things the less I seem to know.
I am working on bolt selection for my 50x50x3mm box section It looks like I can tap this for a secure thread for M5 bolts but if I try to use M8 i wont have enough threads really.
I only thought of M8 as an initial that should look right and M5 sounds a bit small.

Where i'm now getting stuck is:
Is one 8mm bolt as strong as a 5mm bolt in cnc applications when being screwed into 3mm thick steel ?
If not then is 2x 5mm bolts stronger on each corner than 1x 8mm bolt in the centre of a bracket.

I have looked on the web at bolt strength calculators but the numbers they give don't really tell me in a real world situation e.g. 11345nm Strength on a 8mm bolt but I don't have a clue what that means because I have no idea what that really equates to.

I hope this all makes sense

Thanks

Rob