Look in the instruction book, in the inventory of parts it should be specified. Unfortunatly I don't have one; but can try to contact folks who do.

 

The original pistons included in the kit have a bad reputation, which is why I wanted to replace them. The replacement pistons use O-rings, unlike the original ones. As a result, the Aster kit documentation doesn’t include any specifications for the O-rings

 

Red Silicone, 10mm ID x 1.5mm

 

It's a pity Aster Accucraft did not supply these pistons and piston rods to all purchasers of this kit. The people I have talked to with them have all bemoaned the fact the originals leak like sieves.

 

You are welcome..