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Hi STW,
I need to hold a bracket to a sheet of 18mm ply, with a counter M4 bolt, and a nut on the rear. The bracket needs to sit flush with the ply.
Previously, I have used an M4 T-nut on the rear with success. However, this time I cannot access the rear of the board. I would rather not use a wood screw, so am trying to figure out the sturdiest/cheapest/easiest alternative.
Would these hollow wall anchors work?
https://www.screwfix.com/p/rawlplug-hollow-wall-anchors-m4-x-40mm-20-pack/54782
Or do they only work on set thickness plasterboard (for the shoulder to sit inside)? Also, I may need to countersink the plug into the ply a little so that the bracket can sit flush. Would also rather not have to buy the tool for it too.
Any better options?
Thanks,
Duane.
Why the objection to wood screws?
You could use a spring toggle fixing, but then you'll need to drill a wider hole to get it through in the first place.
Insert nut? Again, big countersunk hole needed, don't know exactly how strong they are.
The brackets/fixings may be under quite a bit of force (both tension and shear) - and not sure if wood screws will hold.
You appear to have broken the screwfix site. However, decent woodscrews have a very good hold, just use more?!
Ha yep, Screwfix appears to have keeled over!
Each bracket only takes 3 screws/bolts unfortunately.
You might be surprised what a screw will take. Arguably it's got better purchase on the inner ply layers, rather than a nut on the outer ply. Arguably it's not.
How about a wide coach screw?
You can get threaded inserts for wood, Type D, and can buy them from screwfix but I think the smallest size is M6, so you could open the holes on your brackets. They have a countersunk flange, and need a bit of clearance on the pilot hole depending on wood hardness.
Another possible option is to mount brackets on to a separate piece of ply and then screw this to the board that you can get access to the back of.
Assuming that you have space behind, make keyhole-shaped holes; hole to match nut diameter, 4mm slot below. push the nut (on the bolt!) through and slide down. The shelf/brackets will hide the keyholes