The 22 HP is 12 x 1 mm on the barrel outside and 5.5 x 1.5 for the breech.
The 22 Standard is 10 x 1 mm on the outside and 5.5 x 1.5 for the breech.
I use Viton in 75 duro instead of the factory Buna in 70 duro for better durability. Either should be fine, though.
Bob