Newby questions please be gentle
- Thread starter Dean Grace
- Start date
I'm pretty sure they're 0 BA. It's easily mistaken for 6 mm because it has the same diameter and pitch, but it has a 47-1/2-deg thread angle.
Sorry but your wrong. The speedo mounting studs are definitely 6mm and not 0BA.
The chronometric speedo is completely metric in dimensions and thread form as it was developed by Jaeger in France in the 1920's. Jaeger and Smiths them merged and the design did not change. Even the case if you measure it is metric in diameter (80mm I think) and not 3 inches as most people quote.
Vin998 is correct. This, from the pre-eminent builder and re-builder of Smiths instruments, Mr. D Quinlan.
The Chronometric speedometer is a principle commenced by the Jaeger speedometer company in Paris, France, in the 1920s and as such is a METRIC instrument, that is the dimensions, screws, threads etc are metric and not imperial as generally thought.
For example on the motorcycle instrument, considered to be 3” dia., with a 26tpi thread, the bezel is 80mm dia. x 0.9mm thread
The Chronometric speedometer is a principle commenced by the Jaeger speedometer company in Paris, France, in the 1920s and as such is a METRIC instrument, that is the dimensions, screws, threads etc are metric and not imperial as generally thought.
For example on the motorcycle instrument, considered to be 3” dia., with a 26tpi thread, the bezel is 80mm dia. x 0.9mm thread
Never ceases to amaze me the knowledge among you guys! thanks for the help 
Dean
With reference to the voltage regulator I would recommend the DVR2 from Dynamo Regulators Ltd in the UK.
http://dynamoregulators.com/dvr2.php
You can wire it up for 6v and if later you want to go 12v you just alter the connections to the same regulator you already have. You don't have to buy a different one. It has built in current limit to protect the dynamo, and also has protection against connecting it wrong or connecting the battery the wrong way round. Also it does not get hot so can be mounted inside the Miller regulator case.
I have fitted several and know of at least 15 in operation and have never heard of a failure of any sort unlike a lot of other regulators on the market.
I have no connection to the company, just a satisfied customer.
Cheers
Simon
With reference to the voltage regulator I would recommend the DVR2 from Dynamo Regulators Ltd in the UK.
http://dynamoregulators.com/dvr2.php
You can wire it up for 6v and if later you want to go 12v you just alter the connections to the same regulator you already have. You don't have to buy a different one. It has built in current limit to protect the dynamo, and also has protection against connecting it wrong or connecting the battery the wrong way round. Also it does not get hot so can be mounted inside the Miller regulator case.
I have fitted several and know of at least 15 in operation and have never heard of a failure of any sort unlike a lot of other regulators on the market.
I have no connection to the company, just a satisfied customer.
Cheers
Simon
I know the origins of the chronometric, but there were plenty of decades after that for Imperial threads to worm their way into production. The mounting studs could have made the switch for reasons of production efficiency without affecting any other part of the design. For what it's worth, KTB lists these as BA. However, it's easy enough to put a few of those studs under the microscope to measure the thread form to know for sure, which is what I'll do within the next couple of days unless someone beats me to it.
