Cant get my triple to work right with a double set up, chain rubs when using more of the gears now I have lost one on the front?? My other bike worked fine – need to check when I get home.

Nope, the throw is different IIRC.

the cage is a different width/length.

(not sure throw changes – I’m using a double cage mech/dual chainring crankset with a triple shifter)

The external plate on the mech will be made to match the size of a larger diameter ring, I’ve used a triple front mech in the past on a dual setup and never had any issues with it, it looks a bit odd (when you slide it down the gap will be close to the ring at the front and wider at the rear) and the bike tart in me eventually changed it. I guess in theory the wedge shape left between the mech and the ring could catch the chain but it never happened to me.

Throw is the same on both mechs