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Thread types on No. 199 Fuze


Well-Known Member
Does anyone know the specifications of the thread that is used to screw the aluminium cone onto the top of a No. 199 fuze, and also the thread that is used to screw that base plug into that same fuze? I would like to know if a tap and die for each of those threads could be found.

Also, was there any established standards for threads used on shell case primers, fuzes etc?

Thanks in adavnce for any info.

Prior to the 1960s it was Whitworth form. The actual threads used appear to be bespoke and not follow any of the Whitworth thread form conventions i.e. British Standard Whitworth, British Standard Brass/cycle, BSF etc.

Some of the threads on primers have diameters that defy logic.

A strange mix I came across is the fuze plug on the Red Queen which is 20mm 20 TPI Whitworth form.


Metric/Imperial-Imperial/Metric ?

I agree with TimG as the whole thread system is based on ?
Some threads are "Whitworth" form with imperial dimensions and some seem to be a mixture of metric and imperial in no particular order.

The only thing you can do is purchase a thread gauge for both met/Imp threads and use a vernier caliper to determine the diameter used and treat each thread as a "one off" that way you will have a good deal of success in reproducing the threads.

Best of luck Falcon.
Today I measured the thread that holds the cone on. It has an OD of .842", and uses a Whitworth thread form with 18 TPI. The depth of the thread is .052". I am going to have a go at screw cutting this thread tomorrow.

I will also need to make a new base plug for the fuze. The thread that uses has an OD of 1.583", and uses a Whitworth thread form with 16 TPI. Depth of thread is .060".

As the lathe is in metric (with settings to cut imperial threads), I have had to work out that the depth of the threads in metric. The thread that holds the cone on is 1.32mm. As it is an internal thread, the hole will have to be bored to 20mm. The depth of the base plug thread is 1.52mm, and the OD will have to be turned to 40.2mm

Does anyone have the overall length, maximim diamter and taper angle for the cone? My example is so corroded that measurements will be unreliable.
Does anyone know the specifications of the thread that is used to screw the aluminium cone onto the top of a No. 199 fuze, and also the thread that is used to screw that base plug into that same fuze? I would like to know if a tap and die for each of those threads could be found.

Also, was there any established standards for threads used on shell case primers, fuzes etc?

Thanks in adavnce for any info.

Hi Falcon
Good luck with the threading,as with german threads up to a certain size
i can get away with standard taps and die sets,but after that anything larger although in metric form i have to play around with the screw cutter
with pitch tpi and depth until it suddenly comes together.

Did the british use BSP on any of there fuses or was it just whitworth
or possibley BSF

Best Satan
None of the threads on fuzes I have measured match any thread specifications that I am aware of. They all seem to use the Whitworth thread form, but with unusual ODs and thread depths.
What you guys are talking about here has gone way over my head but it is really good to know that there are at least 4 people left in the UK who know about engineering.
Keep it up!

The knowledge is still in the country but the good old days of "Machine shops" are long since gone !

There are quite litterally hundreds of dfferent threads made by different countries for different purposes and ammo manufacturers were not all that good at "standardisation" even in this country.
199 cone

Good luck screw cutting, when you anounce completion of the cone you're sure to get requests for more repairs and replacement parts, theres lots of people think engineers do it for fun and enjoy the challenge. sorry I've not got a cone to measure but have you tried scaling it off a good illustration? should not be far out especialy if you,ve a couple of dwgs to go on.
I haven't got any drawings or pictures of a good cone. The only measurements I would need are the height and width of the cone, as well as the taper angle. Does anyone have a No. 199 fuze they could measure this off?
Thanks for the link. Unfortunately it only gives the details of the size of the whole fuze, I am interested in just the cap. Would you be willing to part with your spare one?
Thanks for that. Yes, I should be going to Bisley in a couple of week's time. What is the date?
Thanks Dave, would you be able to send a photo of yourself to my email address so I know who to look out for?
Hi Falcon,

Interesting thread!( excuse the pun!!). I got a hold of my No 199 Mk3 fuze which I have had for some time and pulled it apart in order to get the dimensions and sizes you require - this took a bit of doing as it was well stuck with years of Brasso residue!
I agree with your size of the cone thread as 0.842" ( I get 0.843" so we wont argue over one thou! and 0.8438" equates to 27/32" as a fraction). I only have 60 Deg' Unified thread gauges to check the thread form and once again agree with your 18 T.P.I. On holding the thread and gauge against a bright light source I can detect a slight difference in the angle so I agree with you once again that it is a Whitworth thread form of 55 Deg'.
My Zeus book gives the depth of an 18 T.P.I Whitworth thread as 0.0356", so double this (for each side) gives you 0.0712". Deduct this from 0.8438" and you get 0.7726" which is the root diameter of the thread. My aluminium cone thread I/D measures 0.7775" which gives about five thou' clearance, which is just fine. The equivalent metric drill here would be 19.75m/m.

When I measure the I/D of my base plug thread I come up with a size of 1.563". The plug itself measures 1.643" and is threaded as you say 16 T.P.I. Whitworth. With a depth of 0.040" per side doubled up to 0.080" and deducted from the plug diameter it comes in bang on size for the I/D.

As for the aluminium cone itself, it is 2.770" overall in length with a base diameter of 1.846" and finishes off at its top in a 0.375" Rad'.
At the base there is an external spigot of 1.673" Diameter X 0.0850" deep as well as an internal spigot of 1.200" diameter X 0.138" deep.
The angle on the cone measures up at 15.5 Deg'

On the sides of the cone there are two approx' 6 m/m ( probably old obsolete "number" type drill( # 1 = 5.80m/m)) holes situated approx' 0.320" from the base. One of these is 0.280" deep is a blind hole for a key to tighten it onto its mating thread and the other (situated diametrically opposite) is further drilled and tapped for a locking grub screw which appears to be a # 6 x 32 T.P.I. Unified thread, this is 0.300" long and has a dog point at one end and a slot for a blade screwdriver at the other.
(N.B. These holes are drilled at right angles to the centreline of the cone).

Hope this lot helps!
Many thanks Bockscar, that is EXACTLY the sort of information I needed.

Are you absolutely sure that the Grub Screw has a Unified thread? It seems odd that the rest of the fuze would use Whitworth and the grub screw would be unified. Also, what do you mean by a dog point?
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Glad the info' was of help! I can confirm the sizes on the locking grub screw based on diameter sizes alone.....a similar size Whitworth thread has coarser threads. A dog point on a grub screw is where the a portion of the thread at the front of the screw is reduced in diameter - usually to just under the thread root diameter. this reduced section fits into a a suitable drill hole on the component.
There should be a small drill hole on the thread of your fuze where the cone screws onto - this is where the "dog point" of the grub screw locates.
The original grub screw and original drill hole were lost when I drilled out the corroded in grub screw to get the corroded cone off. I drilled down far too deep. On the replacement cone I may just tap the hole for the first available screw brass screw I find. If I don't do it all the way through to the thread on the fuze itself, it would look identical from the outside.