4 replies to this topic

[oldman]

Hi,
Having got my head around metric thread sizes = spanner size
ie M5 tread = 8mm spanner, mate tread = 13mm spanner.
I wondered it was the same with UNC (if thats correct for a mini)
Has someone got a link to spanner, tread, drill sizes?
I have to buy some taps and dies ( I own a mini!)
Mainly to retap rear subframe captive bolts, the ones on the stubby.
Thanks in advance,

John

[Surfbluegarage]

alot of the bolts on the mini are unf threads but with imperial trheads its goes by the size of the threaded section of bolt.. eg. a unf bolt with a head size of 7/16 is 1/4 and so on.. 1/2 head is 5/16 and so on... the read subframe is 5/16s unf too

[dklawson]

I'm sure you can find summary lists online but I'll offer the following quick summary of common sizes.

Fastener diameter --- wrench (across flats)
1/4" --- 7/16"
5/16" --- 1/2"
3/8" --- 9/16"
1/2" --- 3/4"

For the taps and dies, as Mini_Mad said, most are UNF. There is a simple rule for finding the drill sizes needed but you have to know the threads-per-inch for this to work.
UNF Thread
1/4 x 28 threads/inch
5/16 x 24
3/8 x 24
1/2 x 20

To find the tap drill (for 75-80% thread), subtract 1/pitch from the major diameter of the fastener.
For example...
1/4 x 28 = 1/4" - 1/28 = .250" - .036 = .214"
You'll need to round that up or down as necessary to find the closest drill available.

[Ethel]

RDG tools.co.uk

tapchart.pdf (application/pdf Object)

I'm sure you can find summary lists online but I'll offer the following quick summary of common sizes.

Fastener diameter --- wrench (across flats)
1/4" --- 7/16"
5/16" --- 1/2"
3/8" --- 9/16"
1/2" --- 3/4"

For the taps and dies, as Mini_Mad said, most are UNF. There is a simple rule for finding the drill sizes needed but you have to know the threads-per-inch for this to work.
UNF Thread
1/4 x 28 threads/inch
5/16 x 24
3/8 x 24
1/2 x 20

To find the tap drill (for 75-80% thread), subtract 1/pitch from the major diameter of the fastener.
For example...
1/4 x 28 = 1/4" - 1/28 = .250" - .036 = .214"
You'll need to round that up or down as necessary to find the closest drill available.

[Guess-Works.com]

But this is not 100% fool proof, flanged bolts have different sized heads, so for example a 5/16" unf flanged bolt will have a 7/16" head most of the time..

5/16" UNF is the most common thread for those cut in steel/iron on a mini and is that used on the rear subframe mounts.