Whitworth tap nomenclature

Bill D · Oct 19, 2020

I need to buy a whitworth tap. In the USA I would call it a 5/8-11 tap. Is it called 5/8 in Whitworth or would that be too small a diameter? I thought Whitworth was named by wrench size not diameter.
Or could I run a NC die over the bolt threads and use an American nut instead
Bill D.

JohnEvans · Oct 19, 2020

As I recall Whitworth wrenchs were sized by the ROOT diameter of the thread ie the wrench would be marked 3/8 W and a larger number for BS. So yes you are after a 5/8 W tap which is 55*. As to running a 5/8-11 USS die over the thread if it is not a critical app go for it .

awander · Oct 19, 2020

Yeah, you have it backwards. Whitworth wrenches were marked by bolt nominal OD size, NOT bolt head size.

But bolts are referred to by their actual nominal OD.

fciron · Oct 20, 2020

Yup, bolts and wrenches are both referred to by the nominal bolt size, so they match. (The AF measurements are weird 64ths and 32nds, making the system even more convenient.)

5/8" X 11 TPI BSW

Laverda · Oct 20, 2020

If purchasing a 5/8 x 11 BSW tap, make absolutely sure it was not made in INDIA which is where most are made today. Quality can range from OK to absolute crap. They sometimes do not have a radius so don't cut a true Whitworth thread and I have seen ones that are marked BSW that are not 55 degree thread angle but 60 degree. Try to get a tap made in the UK or anywhere but INDIA.

Bill D · Oct 20, 2020

Looks like it will easier and cheaper to make two new bolts in 5/8-11 NC. They are about 9 inches long so I will use allthread and weld on a nut at one end. Only problem is the bolthead sits in a hex well to hold the bolt from rotating while turning the nut. I will have to weld a little extra on the flats so it sits correctly and does not eat the casting. I will try without and see if there is really any problem. The 5/8 whitworth head is just a little bigger then american 5/8 bolt head
Bill D

tdmidget · Oct 20, 2020

So, what is this that has Whitworth threads?

Mark Rand · Oct 20, 2020

If it's only for a clamping bolt, then use whatever you have handy. 5/8"BSW 5/8"UNC or even M16 there's not a lot of difference if they are in a corresponding thread. Hex head is whatever you stick on the end of the bolt. I'd use any of those, since I happen to have taps and dies for them, but they might end up with only a 3/4" AF head, since I've still got most of a bar of EN16T/4130PH hex

Bill D · Oct 20, 2020

tdmidget said:
So, what is this that has Whitworth threads?

1970's Taiwan made mill by Jet. Old enough the motor was cast iron end bells. I am guessing a British Empire hold over.
Bill D..

I will have to shim the bolt head so it does not spin. A Whitworth is 1.1 inch NC is 15/16 wrench. I suppose I could not clean it and use jb weld to fill the gap.

Laverda · Oct 20, 2020

I have seen equipment made in Asia that still uses British threads as is was either copied or made under license. A friend of mine who works on container ships invited me for a tour while the ship was in Long Beach CA for repair. The huge diesel engine was made in Japan under license from a British company. All hardware on the engine was BSW threads. On the side of the hull in the engine compartment were hanging a number of very big Whitworth size tools.

Now I am confused as to what you are working on? It has BSW threads but you are going to use UNC threaded rod and you needed a BSW tap?????

Bill D · Oct 21, 2020

Original plan was to make two new coupling nuts to make them easier to put a wrench on. Then I decided to replace it all with NC stuff. I will try to recut the bolt threads to NC pattern and see if that will work. Only need to cut one flank and I do not have to buy a die. Rolled threads on the bolts will probably not be very concentric and not do well on the lathe while single pointing. All my 5/8 taps and dies are left hand thread for some reason.
Bill D

Limy Sami · Oct 21, 2020

Bill, before faffing around with treading gear, just try winding your Unified bolts in to the WW threads, ...................unless they're close tolerance class, they will more than like fit.
Only when they don't is it time to get the screwing tackle out.

Bill D · Oct 21, 2020

Limy Sami said:
Bill, before faffing around with treading gear, just try winding your Unified bolts in to the WW threads, ...................unless they're close tolerance class, they will more than like fit.
Only when they don't is it time to get the screwing tackle out.

I should have tried that. Poor mans roll forming. Have to get home latter to try. It only needs less then one inch of good threads. A thread file may do it. A acid dip to remove the plating would probably do enough as well.
Bill D.

Mark Rand · Oct 21, 2020

Just don't try it with 1/2" UNC and BSW...

fciron · Oct 21, 2020

Bill D said:
Original plan was to make two new coupling nuts to make them easier to put a wrench on. Then I decided to replace it all with NC stuff. I will try to recut the bolt threads to NC pattern and see if that will work. Only need to cut one flank and I do not have to buy a die. Rolled threads on the bolts will probably not be very concentric and not do well on the lathe while single pointing. All my 5/8 taps and dies are left hand thread for some reason.
Bill D

What the hell?

My shop came with a bunch of oversize left-hand 5/8 inch taps too. There must have been some common application.

Bill D · Oct 21, 2020

I made a tablesaw arbor with 5/8" left hand nut to hold on the blade. It really should have been acme thread but, it works. I also made another with one inch left hand threads for bigger blades. It came with a 1+1/8" arbor and a few blades to match.
Bill D

Bill D · Oct 21, 2020

Thanks Limi! I forced on a NC nut and it works pretty well. I do not have a 55 degree thread gauge but looking at it now it does not look rounded at the tips or in the valleys like whitworth would have. More like the valleys are filled with zinc and it is frosting the tips as well.
I think it is a combination of cheap rolled thread and heavy zinc.
Bil lD

Bill D · Oct 21, 2020

The weird head size threw me off it is too big for whitworth or NC. It may be some sort of heavy head I suppose but not needed in this application. NC is 15/16, WW is 1.0 this is 1.1 so maybe 1+1/8"
Bill D
On edit; heavy hex 5/8 is 1+1/16 so probably that head

Mark Rand · Oct 22, 2020

1.100" is the correct nut size for the original Whitworth standard. BSF fastenings used one size smaller heads, 1.010" for 5/8". During WW2, the standard was changed to use the smaller size for both BSW and BSF in order to save materials.

billmac · Oct 22, 2020

tdmidget said:
So, what is this that has Whitworth threads?

Whitworth threads are more common in modern products than you might think. They are the basis for ISO pipe threads, used world-wide (but not much in USA).

Whitworth tap nomenclature

Diamond

Titanium

Stainless

Stainless

Cast Iron

Diamond

Diamond

Diamond

Diamond

Cast Iron

Diamond

Diamond

Diamond

Diamond

Stainless

Diamond

Diamond

Diamond

Diamond

Stainless

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