Ralph Whitaker Posted June 17, 2020 Report Share Posted June 17, 2020 Still busy putting my TR3a together out of many parts sourced over the last few years. I have a good speedo, the type with the die cast backshell and the studs for the retaining bracket cast in. Looked on Rimmers and they only listed one type, "Brass 5mm" for the large instruments (MM361-020). Ordered 2 which arrived today and they do not fit. Right approx. diameter but wrong thread. Have checked with thread gauge and the studs appear to be 0.195 diameter with a 32 tpi thread. Nearest I can find to this is No 10 A.N.F. Can anyone confirm this as correct, or know the correct thread size so I can attempt to locate a tap and make some myself. Thanks, Ralph Quote Link to post Share on other sites
RogerH Posted June 17, 2020 Report Share Posted June 17, 2020 Hi Ralph, I have found these following threads - M5 0.197OD 31.8 tpi Brass pipe gas thread 0.196 32 tpi Roger Quote Link to post Share on other sites
Ralph Whitaker Posted June 17, 2020 Author Report Share Posted June 17, 2020 Hi Roger, sounds like the metric thread could be on the right track, but I think the thumb nuts from rimmers have been made with a standard 5mm thread instead of the fine thread you have found, my zeus chart only starts at 8mm with the fine threads. It would be logical for it to be metric, as I also bought some alloy 4mm thumb nuts for the smaller gauges and they fitted ok. I will have a look in my Tracey tools catalogue and see if they list the tap size you found. Many thanks, Ralph. Quote Link to post Share on other sites
Ralph Whitaker Posted June 17, 2020 Author Report Share Posted June 17, 2020 Just looked in Tracey tools and 5mm is available in the following pitches,.5, .75, .8, .9, 1.0. Who would have thought that a supposedly standard system would be available in so many pitches. Anyway by my calculations 0.8 pitch works out at 31.9 tpi so I`m going with that. One tap on the way. Quote Link to post Share on other sites
PhilipB Posted June 18, 2020 Report Share Posted June 18, 2020 (edited) Ralph I bought a couple of brass nuts for a temperature gauge a little while ago but can't find the invoice. I think they were 3BA I found this under item 142694350513 on ebay These nuts were used for fixing Smiths and British Jaeger instruments gauges on Austin Healey and MGA cars and are correct for all cars manufactured up to 1962. Set consists of 3 x small and 4 x large nuts internal thread 3BA. Set allows for fixing speedometer, tachometer, dual gauge and fuel gauge. Nut small specifics:- material brass edge knurled outside diameter 9.7mm thickness 4.0mm internal thread 3BA Nut large specifics:- material brass edge knurled outside diameter 12.7mm thickness 4.0mm internal thread 3BA History of Smiths nuts and threads:- M5 x 0.75 - chronometric and aluminium die cast 5 inch cases 3BA brass - up to 1960 3BA aluminium - 1960 to early/mid 1970s M4 aluminium - early/mid 1970s onwards Notes:- 3BA brass and aluminium nuts are interchangeable 3BA nuts were manufactured in large and small diameters M4 nuts were only manufactured in a large diameter M4 nuts original had a straight knurled edge with a groove mid width M4 or 3BA be very careful early/mid 1970s as this is the change over point It does suggest that it's M5 for the die cast speedo cases Hope this helps Phil Edited June 18, 2020 by PhilipB correction of text Quote Link to post Share on other sites
Ralph Whitaker Posted June 24, 2020 Author Report Share Posted June 24, 2020 Thanks Phil, I ordered a 0.8 tap and die, but it was incorrect, your info shows it should have been the 0.75. However I found 1 correct thumb nut, and running the .8mm tap through the new nuts that Rimmers supplies allowed them to go on, albeit a bit slack, but have held OK. Ralph Quote Link to post Share on other sites
Grahamgl Posted June 24, 2020 Report Share Posted June 24, 2020 Ralph, As you say that the new nuts are a bit loose don’t forget to put a spring washer under each nut to prevent the becoming loose due to vibration. Graham Quote Link to post Share on other sites
Ralph Whitaker Posted June 27, 2020 Author Report Share Posted June 27, 2020 On 6/24/2020 at 12:39 PM, Grahamgl said: Ralph, As you say that the new nuts are a bit loose don’t forget to put a spring washer under each nut to prevent the becoming loose due to vibration. Graham I will Graham, but what a pig of a job to fit them. How on earth is one supposed to get at the top 2 wing nuts on the centre panel to tighten them?, and fitting the speedo bracket and nuts with all the steering support brackets and heater support brackets? Also, the wiring on the back of the centre panel is pressing against the heater matrix, should I put something over the matrix to protect them? Ralph. Quote Link to post Share on other sites
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