What are metric drill bit diameters on sale in the UK based on?
In a typical pack I might see drill bits with the following diameters.
I thought those odd sizes were due to some equivalence with inch measurements. But I don't think that is the case.
Nor do they seem linked to the area of the hole cut by the drill bit.
So what are they based on?
I would assume they're based on how many bits they think they can sell you, plus what they have ready supplies of. The sizes seem to match values here quite well:
NT
That's hardly a typical pack. Most just have the 0.5mm increments.
They're not even the tapping sizes for common thread values. Where have you seen such a pack on sale? That might give a clue as to its purpose.
4.2 is for M5 and 3.2 is for 1/8 pop rivets.
It can be difficult to get 4.2 alone so I bought a pack of 10 from SF (lots of 5mm on bikes).
i have a large tray of drill bits i bought in germany from a hobby fair a few years ago, about 300 bits in total, about 10 of each size for the small uns, 5 of the ones over 5mm, and they all go up in 0.1mm steps,
i only bought them 'cos they were a good price, i dont do anything that requires 0.1mm presision with a drill bit, if i need a larger hole than the bit in the chuck, i wiggle it about till i get the requires hole size :)
Have something to add? Share your thoughts — no account required.
Ask the community — no account required