
To eliminate this drawback in order to more reliable bonding of the parts in the hole under the screw it is necessary not just to drill and pre-prepare a place for him to perform one additional operation.
First at the metal sheet of the base panel, or a shelf bracket, as usual, drilled a hole under the screw. But its diameter should be not more than half of the diameter of the shank of the fastener, that is, d/2 (height of screw cutting is not considered). Then a blunt punch with a diameter of d (if sheet thickness is comparable to or larger than d) or with a diameter equal to (d + d)/2 (if the sheet thickness is less than d), carefully punch a hole, pulling and arching wall around it.

The sequence of manufacturing “pukli”:
1 — screw; 2 — thin-walled steel panel; 3 — drill diameter d/2; 4 — a bolt with a pointy tip with a diameter of d(d + d)/2; 5 — attachable to panel detail
The result is a “UCLA” — hole with ribs. Now in the “Pallu” you can boldly screwing the screws and securely attach the item to the panel or bracket. By the way, in a “puckle” (if you will allow the thickness of the ribs) it is possible to cut a thread and screw detail screw.
A. somewhere behind the house Anna