The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Peter Gee on 16.06. 2017 10:08
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Hi, am needing to chase the threads on my type 89 MONOBLOC Jet Block ( the one the main jet holder screws into) but darned if I can imagine what tap they used, and they are not replying from AMAL itself. .the nearest size I seem to get is 19TPI measured on the main jet holder....which would be BSP thread, confusingly there are TWO BSP 19 TPI in tap list named 1/4 and 3/8 . 7/16 x 18 BSF seems close but not correct. The actual thred of the JETBLOCK seems between the diameters of the two 19TPI BSP taps..in fact I get about 0.430 dia when measuring the Jet Holder itself, which is neither one --1/4 BSP x 19 is too small, or the other 3/8 BSP x 18 is too large at over 0.500.... Anyone know?