P-clips on oval tubes

SteK Posts: 148
edited October 2011 in The workshop
I'm making the move to panniers as with winter fast approaching the sheer weight I'm putting in my rucksack is really starting to cause my shoulders to feel like death!

I'm really keen on the Tortec Velocity rack but as I'm putting it onto my 'winter bike' (which is a previous 'summer bike') I'm lacking mounts. So I'm gonna get some P-clips.

The seat stay has a steady 16mm diameter at the bottom of the stay, so no sweat there - however, the top of the stay is elongated so measures 16mm wide but 21mm deep.

I'm not sure what size P-clip I should be putting on it? I'm suspecting if I get something which is the average of the two sizes (around 18-19mm) I should be able to manipulate the shape and make it fit snug - but thought I'd ask here to see what anyone else has done. Or perhaps there's somewhere that makes oval p-clips?

Thanks for reading!

Stephen K