Standard, genuine Fords alloys for Mk6/Mk7 have cylindrical holes for nuts with flat washers. The rest alloys on market sometimes are with conical, sometimes with cylindrical holes.
From thread
posting.php?mode=quote&f=5&p=1257174wojciech wrote:Nuts M14x2mm with flat washers and chromium plated cups for alloys - are available only in Ford shops. And Ford can to impose whichever price. And do it...
You can use for alloys with flat socket standard and cheap nuts for steel wheels plus plastic cups (as on picture). But it looks not so good. Maybe are available plastic cups with chromium finishing for 21mm nuts?
For nuts with chromium plated cups, don't use pneumatic impact wrench, only handiwork set - good, tight 21mm
hexagon-socket wrench and long lever (or for tighter torque meter wrenches). Nuts will be... eternal.
For conical socket is a lot of nuts M14x2 (monolith, chromium) and very cheap.
In UK in Ford shop one nut with flat washers and chromium plated cups costs 9 GBP