This shows the cap and different bleeder valves that are used on a 928.

There are 2 sizes, if 11mm spanner is needed to undo them they are M10x1. If the spanner is like 6 or 7mm spanner then they're M7x1:

113 615 273 A - bleed nipple, M7x1 - 4.28+VAT
357 615 273/1K0 615 273 B - bleed nipple, M10x1 - 4.28+VAT