Stanley bits? 575?

Interestingly I was in Pennyfarthings in Salsbury(UK) - they deal in all sorts of old tools... I had these items with me and asked the guy in the shop if he knew what they were. He had no idea. Anyway, I browsed round the shop and there in a cabinet were the very same items! With a tag saying "Adjustable Bit Gauge - £9.50". Unfortunately no one in the shop (owner away on hols) was able to shed any light on what they are for.

I will return in a few weeks time and discuss with the owner. I wonder what an Adjustable Bit Gauge does... Hmmm...

For info - solved by the guys on uk.d-i-y....

It is a depth stop. Once I had the thing in place I was amazed at how simple it was to adjust and how well it worked. Just slacken off the wingnuts and screw the guide up or down as necessary.