Northland Shooters Supply (NSS) offers knurled thread protectors in stainless and black in the following thread pitches.

Stainless

THREAD PROTECTOR-STAINLESS

– 9/16″-24 (Heavy Sporter and Light Varmint Barrel): $11.99 in Stainless
– 5/8″-24, .820 DIA (Varmint Barrel): $11.99 in Stainless
– 5/8″-24, .930 DIA (MTU Barrel): $12.99 in Stainless 
– 3/4″-24 (MTU or Bull Barrel): $12.99 in Stainless 


Black

THREAD PROTECTOR-BLACK

– 9/16″-24 (Heavy Sporter and Light Varmint Barrel): $11.99 in Black
– 5/8″-24, .820 DIA (Varmint Barrel): $11.99 in Black
– 5/8″-24, .930 DIA (MTU Barrel): $12.99 in Black
– 3/4″-24 (MTU or Bull Barrel): $12.99 in SBlack