I need to tap a hole with a thread of 18mm. What is the tecnical size of the tap required. M?

Thanks Bob

 

Wouldn't that be an M18 tap?

Also you need the pitch of the thread, probably be 1.5mm but thats a guess

 

Standard M18 is 2.5 pitch. For hole size just take the pitch away from the diameter and that will give you the drill size.

M18 X 2.5 = 15.5 hole

M18 fine is 2.0 pitch so you need a 16.0 drill

M18 X 1.5 is a common spark plug size, 16.5 drill

M18 X 1.0 is also avaliable, 17.0 drill for this.

 

M18, that's a suprise

Thanks

 

What measurement is the pitch exactly.

Is it the outer thread minus the inner core?

 

No, Pitch is the measurement from peak to peak.

If you have a rule, measure over 10 pitches, if it's 25mm then you have a 2.5mm pitch!

 

Clever chap

I learnt this some years ago but soon forgotten.