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From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: 8mm / WW tap
Date: Tue, 02 Feb 1999 13:54:25 GMT

It appears I made an error in the metric equivalent of the WW thread.

Somehow, I equated 40 tpi with 40thou which equals 1mm pitch!


40 tpi = 0.625mm pitch

The correct "American" thread for WW collet DRAWBARS** is, according to the
Levin catalogue, faxed to me two days ago:

Catalogue No 0031-01  Drawbar Tap  Type WW   0.275-40tpi NS GH2

No they didn't quote prices!!

**Note this is for Drawbars NOT necessarily the correct spec for male threads
cut on collets etc.

I say this because it is known that the WW threads are originally an anglicized
version of the original 8mm European sizes..of which there are MANY..most of
which are interchangeable with WW collets, drawbars etc.

It is also known that, in order to facilitate this interchangeability..drawbar
threads are purposely cut to maximum sizes

Thus, if you have a drawbar tapped to the above spec..either .275-40 tpi H2 or
the equivalent metric size 6mm x .625mm you can use WW or 8mm collets in it from
all the following sizes are taken from "the Model Engineers
Handbook" by ..Tubal Cain..the other guy..the REAL ONE as someone said!!

8mm collets from Adams, Boley, Boley-Leinen, Coronet, Derbyshire, Pultra and WW
are all threaded  0.268-40  and will all be a fairly sloppy fit in your

8mm collets from Wolf-Jahn are threaded 0.270-40 and will be a little tighter in
your WW drawtube

8mm collets from I.M.E. and LORCH are threaded 0.275-40 (6mm-.0625) and will be
a fairly snug fit in your drawbar.

Now I uderstand the significance of Levin's blurb on the taps "these taps offer
a convenient means of producing the matching threads WITH THE APPROPRIATE THREAD
CLEARANCES" (Caps are mine)

What is the point of all the above?

Somewhat selfish..but hopefully helpful to those who have or contemplate buying
a watchmaker's or other WW/8mm lathe in future. High quality collets of these
types ar BRUTALLY expensive to buy new.  I an most others will collect them
slowly, from a variety of sources and be confronted with a whole slew of
different above, plus many, many more,

It will be a comfort to know that a mixed batch of collets..Boley, Lorch,
Levin,  WW, etc. will ALL fit my Levin Lathe and that I can make a drawbar that
will accomodate them all.

My detailed interest in WW collets started over a year ago when I first
contemplated using them in a Quorn type grinding spindle.  In setting out to get
dimensions ...just of WW collets I ran into a quagmire of conflicting and
simply, missing information. It took until now for me to analyse all the bits
and pieces and be able to set it down as above.

I hope someone else will find it just as useful one day.

Robert Bastow

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