Discussion in 'Engineers' Talk' started by blonker, Nov 17, 2003.
What is the external dia. of M3, M4, M5 6 8 9 10 12 bolts?
3mm 4mm 5mm yes/no
In short yes. But if you are drilling a hole to tap, that is different.
There is a wonderful book you can get called a Zeus Chart which lists (among a million and one other things) the various sizes of hole you need to drill depending on whether the hole is to be tapped or clearance. Not only does it give all the approriate sizes for the M (metric) threads Screwfix sell, but also blasts from the past like Unified, British Association and Whitworth threads. They probably have them on Amazon...
Found my Dads 1976 Zeus Precsion book (Metric Revision). No mention of M3 M4 ect. only I.S.O. metric coarse threads. Assume 2003 edition will have M3, m4 information or are we talking about the same thing
We are talking about the same thing, M3, M4 and M5 are all (as standard) metric course. You will also find (not written in the zeus (i think)) metric fine, these are not standard.
Hope this helps
An engineer of about 25 years (now a chippie)
Metric? Whats that? My Zeus book (bible) is dated 1962. Either I seldom use it or am too tight to buy a new one.
Depends what day it is, mondays is metric, tuesdays is imperial.. and so on, sad i know. but keeps your mind busy
The stated size of the thread M3 , M4 etc is the major diameter. I av been in engineering (37 years). The size of the drilled hole for the tap is always 10% less.
So for M6 threadthe hole would be 5.4mm etc. Always important to drill the correct hole diameter or else the bolt can fail in the hole. Best tap and dies are Lindon brand. Made in Walsall not usual China stuff.
i think you are talking about iso metric threads in which case to get the tapping size you take the pitch of thread away from the diameter and hey presto tapping size
m3 .5 pitch =2.5 hole
m4 .7 pitch =3.3 hole
m5 .8 pitch =4.2 hole
m6 1.0 pitch=5.0 hole
all taps have size and pitch on them hope this has helped
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