Cane Creek Aheadset Top Cap Bolt and Starnut for 1-1/8 Threadless Headsets
£12.48
Cane Creek 40 Series headset top cap, bolt and star nut.
Should be compatible with most treadless headsets with an 1 1/8 steerer tube at the top.
Top quality part not like a lot of these aftermarket types that bend before the headset is even tight.