@mirumir I measured an Optimus 8R and tried to match them to a usable standard metric thread. I Hope this helps Bell Thread measured 11.3mm diameter 26 TPI Calculates to 0.98 pitch A M11 x 1.0 is a sloppy fit but a M12 x 1.0 was too large. Nipple Thread measured 7.6mm diameter 32 TPI Calculates to 0.79 pitch (could be a slight error due to short thread) A M8 x 0.75 worked on this one so should be OK, especially if you use a split die Filler Cap Thread measured 19mm diameter 18 TPI Calculates to 1.41 pitch A M19 x 1.5 should be OK (didn’t have one to try) Good luck
Hello. I am very grateful to you . Another question is the thread sizes, are they the same for 8R, 99, 123? Respectfully
I too am grateful to ROBBO55, that was an excellent answer . -------------- mirumir, given the prev. comments i am sure you meant to say 123R. Yes, the 8R, 99 & 123R tulip & nipple threads are the same between the 3. You already know but for others, re the stout Russian PT1 (8R look alike), the tulip, nipple & filler cap threads all differ from 8r.
Fine ! Thank you so much . Soon I will be able to offer silent burners for 8R, 98, 123R. And separately on Fri 1. Respectfully
Hello . Today, I bought a tap 11/1, cut the thread ... Alas, it doesn’t fit, it doesn’t screw on ... Probably, you need to look for an inch tap.
@mirumir we're into day 5 on this. i was not clear on your objective but your question was straight-forward. being war-torn Ukraine i felt some urgency with this. 24hrs after your question, for tulip i gave "answer: 7/16x26tpi, a thread size [in US] you would need to special order." ---------------- i should have suggested sooner, posting pics is most effective approach when requesting assistance, certainly in this case. re tulip thread: ROBBO55 "26 TPI Calculates to 0.98 pitch, A M11 x 1.0 is a sloppy fit" clearly having a close review on your behalf. vs your result in-hand: I bought a tap 11/1, cut the thread ... Alas, it doesn’t fit, it doesn’t screw on ... To clarify your are saying your newly cut M11/1 female thread did not screw onto an 8R burner? 2 different results. ROBBO55 tested thread, with a tap, the opposite way (tap into tulip), sloppy fit result, for me, it does not seem the difference is strictly his approach. (due to sloppy. if it were tight fit a tap may go where bolt will not. he reports M11/1 is sloppy fit. his result inline w/my expectation, as I tried M12 into 8R tulip. the bolt was just a tad too big). We have to wonder what is amiss? ONE thought: You are familiar with PT1 (8R copy) we have established. FYI there are as many as 6 other 8R copies all or most are Asian, those can be seen in this thread: 8Rs and 8R-like stoves we have not seen any pics, are you sure it is 8R burner if that is what you have? i guess i do not know what you have in-hand. I presume it is clear we do want to help you. --------------------- Your objective is to sell parts... "... be able to offer silent burners for 8R, 98, 123R. And separately on Fri 1. [PT1?] Respectfully..." cc: @ROBBO55
You have the male thread. Look up the "Three Wire" method of thread pitch measurement. Measure the number of threads per inch.
Hello . Thanks for the help, anyway. I am very pleased that people responded and want to help. I understand that the 8R comes in several varieties and the threads may vary. I tried on the original 8R (with an iron key) I will try to order 7/16 26 inch taps - this will be the best option. Thread 11/1, cut on a lathe on a washer 5 mm thick. Once again, thank you all for your help and Happy New Year! Peace, Health and Success!!!
Prayers hence. Heavenly King, Comforter, Spirit of Truth, who are everywhere present and fill all things, have mercy on us and save us. Gospodi pomiliui. Good luck.
Greetings to all ! I did not find a tap with a 7/16x26 thread in the catalogs. there are 7/16x20 and there are 7/16x28. Unfortunately, 7/16x28 is very rare, and it is extremely difficult to buy it. I ordered 7/16x20. I will try . Respectfully to all
@mirumir I bought my 7/16 26tpi tap and thread from England. It was a specialist business. I will look for the information to send to you. Keep safe & best regards, Tony
@mirumir OK, I went back to look at the stove again. I have a 7/16” x 26tpi BSB (British Standard Brass) tap. It screws comfortably into the burner bell. Good so far. I then tapped a piece of 3mm brass with the 7/16” x 26tpi BSB tap. It screwed onto the burner spigot 2/3 turn then locked. I couldn’t get it to go any further. Suspecting the tap was the problem I contacted @Tony Press and asked him to repeat the procedure. He came back with the same result. I tried a die on the spigot thread but stopped when it started to remove brass. SO One possibility BSB has a 55 deg profile and the Optimus thread is 60 deg. If so, a 7/16” x 26tpi BSC (British Standard Cycle) tap could work? But I don’t have one to try. @Colin Geer or anyone else have a 7/16” x 26tpi at 60 deg profile to try? The other possibility The thread isn’t 7/16” and this has just been a convenient size for cleaning existing threads. 7/16” converts to 11.11mm. I measured 11.33mm dia on the thread of two Optimus 8R stoves. I would normally expect to measure slightly smaller than the nominal size rather than slightly larger. From previous discussions we know many of the Swedish threads are not standard and this could be one. At a guess nominal 11.5mm x 26 TPI or M11.5 x 1.0? Happy to be proven wrong.
I can confirm that the British Standard Brass BSB 7/16 26tpi tap will not produce the correct thread on new brass for the Svea 123 or Optimus 8R. It is ok for repairing damaged threads on a burner bell: But a new female thread will not fit the vapouriser thread: Tapped with BSB 7/16 26tpi tap. Will not fit this. Best regards Tony
