A:
The Safco 4224 and 4225 hooks come with 2 different size L-shaped brackets and covers that are installed on the hook unit one way or the other for the following panel thickness parameters: (1) 1.25" to 2", (2) 2" to 2.75", (3) 2.75" to 3.5", or (4) 3.5" to 4.25" - you may be able to get the "Mounting Instructions" sheet #4224-37MP from Safco which would help you understand: Safco - 800-664-0042. The frame is metal with plastic covers and the hooks are plastic - appears to be a nicely made unit. Just received today so don't know how it will hold up.
Answered on 2/9/2011 by Shopper for the office from Blacksburg, VA