Two of the Manfrotto 635 Quick Action Super Clamps cannot be used alone to connect a crossbar to autopoles or stands. Two of the Manfrotto 038 Double Super Clamps (B&H # MA038) are a better choice.

Yes, all 5 screw holes on the bottom of the Manfrotto 635 Quick Action Super Clamp are 1/4 thread.

You can use a Superclamp with flat or round surfaces.

It will clamp to any pole or column under 1.75". Just be careful not to crush the carbon fiber as these clamps to have a good amount of clamping force.

Very similar products. I like Manfrotto as a company because they seam to be very meticulous with their products in general. The lever gives you great power and they do ship their 035 model with the stud. Does the Avenger model come with a stud? I did not get the impression I would have as much clamping power with the rounded knob from Avanger. I hope this helps you in making a decision Good luck

There are five holes arranged in a quincunx. I find the central hole is UNC 1/4" 20. One pair of opposite holes appear to be M5. The other pair seem unthreaded. Perhaps alignment holes for an unknown accessory? I would like to find proper specs for these holes.

The Manfrotto 035RL Super Clamp with Standard Stud can attach to a 2x6 beam, but one should use a safety cable like the Impact Safety Cable (18"), B&H # IMSC1.518 (https://bhpho.to/3Yg3t0L).

if you purchase the Impact Short Double Female Stud for Super Clamps with 1/4"-20 & 3/8"-16 Threads, B&H # IMSRP103, you should be able to connect the Manfrotto 035RL Super Clamp with Standard Stud to the 1/4"-20 or 3/8"-16 male thread on the top of your tripod head.