This is the one used in the testing, appears well made and sturdy. The specs on size are in the description. Recommend you do not overtighten. We torque these to 13.6 NM or 10 ft lb but we also use some hylomar (Megadan's idea) for sealant that provides some extra holding power.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1