My goto is either the metal homedepot one for barhangers or the carlon or allied saddle plastic box. The PnS one was always to expensive at my supply house.
When that happens to me I always think (and sometimes say) "why'd you ask if you didn't want my answer? "
Yeah, I got a cousin that likes to do his own wiring, but his wife doesn’t trust his wiring, and will not let him energize it until after I look at it. He built a new living room addition to his house, not very big, about 12x16. He wanted two ceiling fans, each on its own 20 amp circuit, with a switch for each on opposite sides of the door. Why? He thought two fans would be too much on a 20 amp circuit! He kept arguing with me about just using one circuit, and put both switches on the same side of the door. Easier to do, less wire, and oh! He wanted to use a couple of used plastic boxes to hang the fans from! Haven’t been back, though he calls twice a week wanting me to come back. That’s another reason why I hate residential. If he wasn’t kin, I would have turned him down at the beginning! Hoping he will get the hint and call somebody else. His sister’s husband is an HVAC guy, and he will not answer the phone for any of his in-laws calls (five brother in-laws, and three sister in-laws)
I have seen one box that used 8-32's, black ones that came with it. Must have been tempered screws. Saw it on a shelf, didn't use it. Can't recall the brand, was nonmetallic.The first box:
Phillips-head screws (#10-32 x 3 inch) mount the fan or fixture directly to the metal bracket.4-inch Round Ceiling Box | Ceiling Boxes | Electrical Boxes | Wiring Devices
Ceiling Fan Box, Premium Grade with integral fan mounting bracket and four Auto/Clamps. 12 pack.www.legrand.us
The second box seems sketchy.
The non metallic box is supporting the fan/fixture and the holes are only 8-32. I have never seen any fan box that uses 8-32 screws. Most are 10-32 and occasionally 10-24.9350-FANVB :Allied Moulded Products
alliedmoulded.com