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WW1 German Fuze threads
- Thread starter DICKAREN
- Start date
Hello Richard,
this question is exactly my area.
They are "metrimperical"
which means: metrical diameters with imperial pitches. And not only the screws but all threads. I never discovered a WW1 german fuze thread with metrical pitch.
I just made a thread tap at home for a 3,5mm x 1/38" set screw thread because such taps are not available anywhere. Other examples are:
2,5 mm x 48 tpi (set screws for K.Z.14 top cap -> example picture attached)
3,2 mm x 38 tpi
4 mm x 32 tpi
If you tell me which screw thread your are exactly looking for I might be able to look up official dimensions.
I never found out if we had a standard for such screws or if each factory made there own (I couln't imagine that)
Following France we started to metricalize in the 1860's and until the 1870's length meassurements became metrical in most areas of the life. But the machines like lathes still were imperial and could not be converted quickly because such a conversion is always a collaboration problem when not all factories convert to metrical system from one to an other day. And also internationally the metalworking industry was much influenced by British and US companies which used the imperial system so simply no metrical tools could be bought on the international market at this time.
Germany started to use the metrical thread pitches in the 1920's and in 2nd WW especially for fuzes most of them were fully metrical. After war special areas like electrical installation equipment became metrical. And even now we still have imperial therads in water pipes for example. Sometimes Withworth threads are still used today when it's 55° angle has advantages compared to the 60° angle for some application.
this question is exactly my area.
They are "metrimperical"
which means: metrical diameters with imperial pitches. And not only the screws but all threads. I never discovered a WW1 german fuze thread with metrical pitch.I just made a thread tap at home for a 3,5mm x 1/38" set screw thread because such taps are not available anywhere. Other examples are:
2,5 mm x 48 tpi (set screws for K.Z.14 top cap -> example picture attached)
3,2 mm x 38 tpi
4 mm x 32 tpi
If you tell me which screw thread your are exactly looking for I might be able to look up official dimensions.
I never found out if we had a standard for such screws or if each factory made there own (I couln't imagine that)
Following France we started to metricalize in the 1860's and until the 1870's length meassurements became metrical in most areas of the life. But the machines like lathes still were imperial and could not be converted quickly because such a conversion is always a collaboration problem when not all factories convert to metrical system from one to an other day. And also internationally the metalworking industry was much influenced by British and US companies which used the imperial system so simply no metrical tools could be bought on the international market at this time.
Germany started to use the metrical thread pitches in the 1920's and in 2nd WW especially for fuzes most of them were fully metrical. After war special areas like electrical installation equipment became metrical. And even now we still have imperial therads in water pipes for example. Sometimes Withworth threads are still used today when it's 55° angle has advantages compared to the 60° angle for some application.
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Hello Richard,
really funny, actually I have absolutely the same patient in my hospital even from same manufacturer and also need the same parts plus the large top iron screw. It will be one of my next projects.
I only found meassurements of the two grub screws from top of the "Dopp.Z.15 umg. (E)" which is the late war iron variant of the fuze so meassurements are without warranty. The meassurements are for the thread in the hole and not for the screw itself. The screws have slightly smaller diameters for tolerance.
The two holes for the grub screws on the top: 6,1 mm diameter / 26 t.p.i. and they are of a special "Flachgewinde" = "square thread" type (flank angle 0°). I guess the screw had then 6 mm diameter. The rest is some calculation: 1" = 25,4 mm / 26 = 0,97 mm / 2 = 0,49 mm thickness of the thread profile. If you make the cutting tool for the lathe a bit wider around 0,54 mm then the screw won't jam because theres some space in between internal and external thread. The cutting depth of square threads is the same as the pitch I think but cutting the screw slightly deeper also will prevent jam. On the attached picture the shape of this exotic thread is visible...
The screw from the side I can meassure on my example tomorrow if you like. It's is still in useable and screwable condtion.
really funny, actually I have absolutely the same patient in my hospital even from same manufacturer and also need the same parts plus the large top iron screw. It will be one of my next projects.
I only found meassurements of the two grub screws from top of the "Dopp.Z.15 umg. (E)" which is the late war iron variant of the fuze so meassurements are without warranty. The meassurements are for the thread in the hole and not for the screw itself. The screws have slightly smaller diameters for tolerance.
The two holes for the grub screws on the top: 6,1 mm diameter / 26 t.p.i. and they are of a special "Flachgewinde" = "square thread" type (flank angle 0°). I guess the screw had then 6 mm diameter. The rest is some calculation: 1" = 25,4 mm / 26 = 0,97 mm / 2 = 0,49 mm thickness of the thread profile. If you make the cutting tool for the lathe a bit wider around 0,54 mm then the screw won't jam because theres some space in between internal and external thread. The cutting depth of square threads is the same as the pitch I think but cutting the screw slightly deeper also will prevent jam. On the attached picture the shape of this exotic thread is visible...
The screw from the side I can meassure on my example tomorrow if you like. It's is still in useable and screwable condtion.
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Pretty much 3/4 inch. An off the shelf die can be bought from https://www.tracytools.com/taps-and-dies/20-TPI-CYCLE-PITCH ?product_id=1005
At the time, might the various designs have simply used standard British Imperial tool measurements, rather than some non-standard metric dimension (assuming say 18,8mm is not a standard)?
The egg grenade fuzes seem to be 1/2 inch BSW, unless they are actually something obscure but very close to 12,7mm.
Also the grub screw in the top of a M1914 rifle grenade fuze is 1/8 inch 40 tpi Whitworth form, or at least that thread of screw fits perfectly if you happen to be missing a grub screw.
The egg grenade fuzes seem to be 1/2 inch BSW, unless they are actually something obscure but very close to 12,7mm.
Also the grub screw in the top of a M1914 rifle grenade fuze is 1/8 inch 40 tpi Whitworth form, or at least that thread of screw fits perfectly if you happen to be missing a grub screw.
Another example of "metrimperical" is German artillery primers, which up to 1945 were metric, but Whitworth form and threads per inch. Non military is the PG thread on electrical conduit that apparently survived until as late as 2000, metric diameter, threads per inch, (however, used an 80 degree thread angle).
The practice is not confined to Germany, the PRF thread in the British "Red Queen" projectile (1950s) is metric diameter, Whitworth form and threads per inch.
TimG
The practice is not confined to Germany, the PRF thread in the British "Red Queen" projectile (1950s) is metric diameter, Whitworth form and threads per inch.
TimG
No it's not standard it not even have 55° angle but 60°. Our old threads of fuze parts and also the fuze main treads are all very, very "special". Flank angles go up to more than 70°. The worst is the old prussian percussion fuze thread. It has an official pitch of 10 + 10/11 inch (see attached image). That would be 10,91 t.p.i. I tried to cut a thread with 11 t.p.i. and it screws in well in a 10+10/11" hole. All other threads had even pitches but many different angles/diameters.
Your are right about the egg grenade fuze hole, it's half inch BSW officially but it's an exception. About the rifle grenade I don't know because I didn't see an official manufacturing drawing.
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...another nice example are the british and american 37 mm common shells which had the original Hotchkiss fully metrical thread M14x1,5
