Oh dear. The sizes above are from their Pro 5000 range. The sizes for their 'standard' racing brakes are shown below. Even more choices = even more confusing!
No. of Pistons/Option/Piston Ø (mm)/Disc Size (mm)/Disc Th. (mm)/Mount Type/Mtg Hole Ø (mm)/Mtg Offset (mm)/Mtg Centres (mm)
4 / Option 3 / 2x 28.6, 2x 34.9 / 330-355 / 28-32 / Radial / 12.15 / 44.1 / 152
4 / Option 4 / 2x 28.1, 2x 44.5 / 330-355 / 26 / Radial /12.1 / 42 / 180
4 / Option 5 / 2x 28.6, 2x 36.0 / 356 / 32 / Radial / 12.15 / 42 / 180
4 / Option 6 / 2x 28.6, 2x 36.0 / 356 / 32 / Radial / 12.15 / 62 / 130
4 / Option 7 / 2x 36.0, 2x 44.5 / 295-355 / 28-30 Radial / 12 / 44 / 152
4 / Option 8 / 2x 27.0, 2x 34.0 / 310 / 27 / Radial / 10.15 / 45 / 130
4 / Option 9 / 2x 28.6, 2x 36.0 / 356 / 32 / Radial / 12.15 / 40 / 210
4 / Option 10 / 2x 34.9, 2x 41.3 / 285-355 / 28 / Radial / 12.15 / 35 / 180
4 / Option 11 / 31.8 / 285-355 / 28 /Radial / 12.15 / 35 / 180
4 / Option 12 / 31.8 / 285-355 / 28 / Radial / 12.15 / 35 / 180
4 / Option 13 / 2x 27.0, 2x 34.0 / 300 / 28 / Radial / 10.15 / 35 / 180
4 / Option 14 / 2x 34.9, 2x 41.3 / 280 / 28 / Radial / 9.7 / 44.1 / 152
4 / Option 15 / 2x 34.9, 2x 41.3 / 280 / 11.5-25.4 / Radial / 10.2 / 22.0 - 30.0 / 152
4 / Option 16 / 2x 38.1, 2x 44.5 / 280 / 30 / Radial / 10.2 / 48 / 152
4 / Option 17 / 2x 34.9, 2x 41.3 / 278 / 16-17 / Radial / 10.2 / 40 / 120
4 / Option 18 / 2x 26.0, 2x 31.8 / 278 / 16-18 / Radial / 10.15 / 40 / 120
4 / Option 19 / 38.1 / 267-295 / 16-18 / Radial 10.2 / 37.25 / 130
4 / Option 20 / 31.8 / 267-295 / 16-18 / Radial 10.2 / 37.25 / 130
4 / Option 21 / 2x 38.1, 2x 44.5 / 295-356 / 32 / Radial / 12.1 / 42 / 180
4 / Option 22 / 2x 38.1, 2x 44.5 / 332 32 / Radial / 12.2 / 42 / 180
4 / Option 23 / 2x 38.1, 2x 44.5 / 332 32 / Radial / 12.15 / 42 / 180
Again, courtest of Demon Tweeks
http://www.demon-tweeks.co.uk/motorsport/brake-calipers/a-p-racing-brake-calipers