Dears, I took: a 7mm x 24tpi and 26tpi Whithworth thread checking tools/combs, M7x1mm comb and M7x1mm die. I tried them on: - approx. 5 modern new, Chinese Px jets, - one NOS 200 Radius jet, - several used 500 Px jets, quite old and most likely “made in Germany” - three used, old 300 Optimus jets from very old lamps (but I can not be sure about the jet age) - approx. 8 old, used Petromax jets from WWII lamps : most of them 200 and two 300 INHO: - 26 tpi does not fit well any of jets. Well, it might be “OK fit” in some cases, but other combs fit better in every jet - M7x1mm fit quite well, but does not reach the end of the thread. Somehow fit is not tight. It might be that 55 vs 60 pitch angle difference - 26tpi Whithworth fits the best all jets. Surprisingly M7x1mm die does not fit any of jets fully to the end… this is new die and I was not able to thread it to the end of any jet – new, old, NOS, any. Please try yourself with any jets and M7x1mm die and let me know. Please bear in mind that most of jets were used, my experience is limited and feelings/judgments subjective Not sure if attached pics can explain anything (Petromax jets – two 200 and one 300), but I did my best. Thank you all for your input. @Jörg Wekenmann - if you can share a Hasag jet drawing/info then please do it - sooner or later we will discuss Hasags . I have four wrecks of Hasag 102 waiting to fettle and had some problems with jets already Have a great day, Piotrek
Not quite clear. Was it the Whitworth 24tpi or 26tpi? Which one actually fitted better on your checks with the thread gauge? For info, checks using an actual threading die isn't recommended because you can unintentionally cut the jet samples further just by screwing them in. Instead, use the metric M7 x 1,0mm thread gauge for this:- like what you've done using the Whitworth gauge.
Oh sorry - 24tpi Whithworth fits the best all jets. So this is in line with Optimus drawing. I used the metric M7 x 1,0mm thread gauge for tests. Just additionally I checked if M7 x 1,0mm die will fit and it did not.
So...it seems highly probable that the 7mm x 24tpi Whitworth thread size could be what the original jets of the Petromax 200hk and above be having. Perhaps other members might have NOS parts for verification. I'd might try to get a brass plug made to that size for later fit-checks. For those who have access to a lathe, making an external thread without a real die should be less difficult than making an internal thread without a tap.
@MYN - you can also check new modern jets. I buy mine from Petromax.de shop. You are much more experienced to judge if these have Whitworth or M7x1mm thread.
I have used the 7 x 1mm taps to repair holes on the generator. The jets have fitted reasonably well on those. However, those are not pristine NOS parts. The 7mm x 1,0 is already widely accepted. I'd be more interested on others' opinion on the W7-24tpi thread instead. It could be the actual real deal but had been somehow obscured over the years.
