Identifying rear triangle material

[Rich Aitch]

And what the hell is Raleigh ATT 27? A lot of 90's Raleighs seem to be made of it. I'm guessing ATT means All Terrain Tubing?

I assume it was Raleigh's own spec of high tensile tubing. I used to think that ATT 23 or ATT 27 was short for 1023 and 1027 grades of 1020 [High tensile] steel. But as far as I can tell there is no such thing as 1023 and 1027 steel.