Identification xx

[Alex kettle]

Been on the forum a while now and haven't put anything up or progress of my rebuild of my dads a10 that he has given me so far, and that's all about to change now I've managed to work out resizing images on my iPhone.
First one then any idea on the two xx above the std stamp. The old man says it might be something to do with ratios but couldn't shed any more light on it. I'm sure one of you will know.
Thanks

[Stephen Foster]

I have a plunger gearbox with the same markings .
I think it may be an inspectors mark as the STD denotes standard ratios .

[BSA_54A10]

If you look closely you will find dozens of numbers & letters stamped all over the place.
Back in the day, machining was done between stops or off a cam thus no two parts were ever machined identical ( tools wear, pick up on the tip, job gets hot etc, wtc, etc.
So when a part was "finished" it got checked using go - no go gauges.
the one that fitted best got it's number stamped onto the part.
So for your gearbox either 2 measurements were X or the XX gauge was the best fit.
Some cases were stamped on both 1/2s so they could be mated again after line boring.

[Alex kettle]

Thanks for your responses. Was just curious really. Nice to know though and goes to show the wealth of information known on this forum.