The double bolt clamps feature a bolt on each side of the clamp. This allows the clamps to evenly distribute the pressure between two bolts instead of one. The butterfly clamps are more prone to failure and when they do fail they have nothing to hold them together. The double bolt clamps are also a lot more reliable with maintaining a seal. Tighten the bolts on both sides of the clamps evenly. Tighten them until they squeak a little, and you are good to go. The butterfly clamps tend to loosen up and tend to need to be re-tightened a few times during extraction.
Posted in: Bolt and Clamp Specifications