Plastic Bolt protective covers. Made from PE plastic. Good Good quality.
eBay
Bike Fork Steerer Headset Stem Top Cap Carbon Compression Plug Star Nut Adjuster Expansion Bolt Bicycle Headset Expansion Screw
Aliexpress UK
Versatile: These hinged screw covercap are designed to provide for protection to exposed M5 screw heads, making them versatile for both indoor and outdoor use. They effectively conceal screw heads, leaving a clean and aesthetically pleasing finish.
eBay
M6 Grade 12.9 Black Hexagon Hex Socket Head Cap Allen Bolt Screw Over Ultra Long 100 105 110 115-400mm Half Thread Carbon Steel
Aliexpress UK
Quantity: 160pcs. Size: M4 M5 M6 M8 M10 M12. Type: Bolt Covers. Material: Plastic.
eBay
RISK Bike Bicycle Titanium Alloy DUB Crank Cover Cap Crank Arm Screw Bolt Crankset Set
Aliexpress UK
The cap will attach to the hexagonal part of the screw covering the screw head and washer if attached.
eBay
STONEGO 50PCS Plastic Screw Caps Furniture Hardware Bolts Protective Covers Snap on Nuts Decorative Accessories
Aliexpress UK
12mm are for bolts requiring a 19mm spanner.
eBay
Risk RA112 Mountain Road Bike Bicycle Carbon Fiber Cycling Headset Stem Top Cap M6x30mm Titanium Bolt For 28.6/31.8 Front Fork
Aliexpress UK
Screw size: M3 x 25mm. STAINLESS STEEL DECORATIVE.
eBay
Bicycle Headset Spacer 5mm 10mm 20mm Headset Top Cap bolts Alloy Aluminum CNC Made colorful bike parts
Aliexpress UK
They effectively conceal screw heads, leaving a clean and aesthetically pleasing finish. Versatile: These hinged screw covercap are designed to provide for protection to exposed M5 screw heads, making them versatile for both indoor and outdoor use.
eBay
Grade 12.9 M6 Black Hexagon Hex Socket Head Cap Allen Bolt Screw Over Ultra Long 100 105 110 115-400mm Half Thread Carbon Steel
Aliexpress UK
Quantity: 160pcs. Size: M4 M5 M6 M8 M10 M12. Type: Bolt Covers. Color: Black.
eBay
Left-Handed Thread Hex Allen Socket Cap Head Screw M4M5~M16 Grade 12.9 Black Carbon Steel Reverse Thread Hexagon Hex Socket Bolt
Aliexpress UK