I spoke to our buyer and we generally look at many things when pricing an item, making sure B&H is always offering the best value and most competitive price. Currently, the 40 is a fantastic deal and its not that they are both the same price but we are able to offer a better deal on the 40.

You can use an Atlas 8d tube (threaded ends-sold on B&H). Place the main portion of the tube in the Gobo head. Using a mic mount you can add a Rode shotgun/Senheiser/or Shure mic to capture your sound. Use one of the open holes on the Gobo head to thread your mic cable through (XLR or mini 8) dependent on the type of shotgun mic you use. As Royce had said in the previous answer, there are a number of ways to mount this. Good luck with your rigging.

3 lbs (to nearest ounce).

It is compatible but if you use it extended it might tip. And in general I would use it with a sand bag.And if you do you should use it with another grip.Note that an arm like that is not made for heavy items like studio strobes. It is really made for cards, gobos and smaller lights like speedlights.For heavier items it is best to use a boom. And those can be boom arms, boom kits or boom stand combos. But the boom arms you should use a heavier and stronger stand.

For this inquiry, it would be best to contact the manufacturer, Impact, for further assistance at 212-594-2120.

The knuckle offers a 5/8" and 3/8 opening in order to attach to the top of a light stand.

The knuckle is fixed in place at the end of the rod.

Ya, I've done it plenty and it works great.