I've assembled the bogies, but in the process I've mixed them up and can't ascertain the difference between the ones assembled with part A11 and the ones assembled with A12. Is there a difference in these parts? Test fitting to the hull I really can't tell (one bogie seems to fit in either slot for assembly E or F, it's obvious where the D bogies go) but wanted to know before I committed to anything.

It's hard to tell from the perspective that the instruction uses. The only difference between the E and F bogies is that one part. I am guessing it has to do with some left/right asymmetry, like placement of the A36 or the length of the two arms.

I compared A11 and A12 side by side under magnification and I could not spot a difference. I kept them lined up carefully so I put the 'right' ones in place, but I'm betting they are identical and just happened to have different numbers. Who knows, maybe they figured at first that they would be different and in the final version, not so much! I'm going to check one more time since I'm still in the process of building...

You might try tacking them on then fitting the side plates (I take it that is the purpose of A36). Maybe the spacing of them is a wee bit different?

Well I was wrong! There IS a difference.

Look at the mounting for the idler. There is a molded flange around it with tiny bolt detail. A11 has the flange ending right at the top of the part, whereas A12 has a wee bit of overlap showing above the flange.

A11 goes in the middle of the 3 bogies.

I should take pictures to make it clear...

Actually the whole idler mount is slightly lower on A12!

That's a return roller actually. The idler is at the front
And is used to keep the track in tension.

Pleased that you worked it out anyway.

Well you people friggin rock! And thank you for the visual Nick, that takes the cake!

Well DOH! of course it's a return roller. Totally spaced there...

bloody 'ell, never noticed that. I imagine it's the same for my Mk10. looking at ordering up a 5 in a coupla weeks or so. actually, it's a return roller, not idler