Something trivial has been bugging me, and comes up fairly often on various BBS. Moss Motors part number 461-560 - LAYSHAFT, for laygear, MGA and early MGB gearbox. In the Moss MGB parts catalog it is noted as being 0.643 diameter. It is actually 16.4-mm maximum diameter (0.6456" max). Tolerance range can be 0.6455-0.6450, so it should be noted as 0.645 diameter rather than 0.643.

There have also been lots of prior notes about soft shafts with very high wear rate and very short life, sometimes less than 10,000 miles. A standard simple check is to run a file or hacksaw across the OD (in a non-bearing area). File should not mark the surface if it is properly hardened. Some people are sending the new layshafts out for additional surface hardening, which makes for a huge increase in cost of the shaft. So I put this question to Moss Motors with the following reply.

On 6/5/2010, Michael Grant from Moss Motors wrote:
"The layshaft we were buying back in 2005 was checked against an original layshaft and we determined that the hardness and dimensions were not as consistent as they should have been. We actually blocked sales from 7/19/05 to 8/24/05 while we found another supplier. We did find a source in the UK and we have been buying shafts from them since. The change in vendors raised our cost significantly and we raised our prices to compensate. We have the ability to "lock" purchasing to a single source to prevent filing in with what may be inferior product and we have done so.
John Twist returned a shaft in September 2007 that had been installed in a customer's car in December of 2006. He felt the shaft was worn excessively, and John was sure the shaft came from us; but it is unclear exactly when it was purchased. We had that shaft tested when it came back and it was 24 HRC. Concerned, we checked our stock - new shafts pulled from stock 19-Sept-07 averaged 59 HRC. It is very likely that the failed shaft was from the pre-2005 source. Nevertheless, we will not take a chance with this layshaft.
This part is still inspected every time they come in. We measure the OD and the length (both overall and to the step) of every layshaft received. Any found to be too long are sent to our shop to be machined. A random sample are tested for hardness. The results are entered into a perpetual spreadsheet. As a result of the steps taken, we have a high degree of confidence in the shafts we are selling".