Hollow Wall Drive Anchors


I have lath and plaster walls. I want to hang 3 shelves that have hangers pre molded in the back of the shelves that requires the shelve be placed over an extended screw head and then pushed downward so that screw head slides into a slot about a 1/2 inch long and come to rest at the top of the slot. Hope I described that in great enough detail - if not ask questions!
I went to Lowes to purchase Hollow Wall Drive Anchors and it turned out I seemed to have more knowledge about what I wanted than any of the employees. Not enough to actually know what I wanted though. Very, very sad for Lowes and me too!
Anyway I purchased some anchors made by Cobra. The anchors are not like other hollow wall anchors I have used in the past in that they do not require a pre-drilled hole. Supposedly one should hammer the anchors into the plaster wall. The anchors are equiped with a metal point and a plastic collar just above the metal tip. Anyway, these things are at least 1/4 inch thick at their widest so I thought rather than just pounding them in I would pre drill a hole to reduce the tension when inserting the anchor. Any thoughts?
My nagging question is, have I purchased the correct anchors? There is a selection guide on the packaging.
SIZE WALL THICKNESS 1/8" SD 1/8" @ 1/2" 1/8" LD 5/8" @ 7/8" 1/8" SLD 1/8" @ 13/16"
I purchased the 1/8" SLD - which was anchor that was finally recommended by the store employee. I do not understand what the manufacturer is trying to demonstrate by the 'wall thickness' in the chart above descriptions. What means 1/8" @ 13/16" under Wall Thickness?
Thanks for any assistance!
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Sounds like the shelves have "keyhole" slots. If it's not wood lathe plaster, a molly bolt would work well

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It is wood lath - house is over 40 years old.

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The "wall thickness" issue is for using these "moly" anchors in various types of walls. Typically, for modern dry wall it is 1/2" or sometimes 3/8". For things like cored doors, which are 1/8" masonite, you use smaller ones.
The lath/plaster, is going to be 1/2" or so, I would think. I've never pounded in the ones you describe, but drill a hole -- typically 1/4", and then use a hammer/mallet to coax them in. If you have trouble with them turning, as you tighten down the screw, then there is a little tool that engages the two notches on the flange of the moly. NO idea where I picked that tool up, but in a pinch, a pair of needle nosed pliers will do the trick. Then, when you have them in (do NOT over tighten, or you can sheer the screw off!), then back the screw out enough to engage the slots in the back of the shelf. You may have to fool around a bit with the length of the screw to get a nice fit to the wall. It is very important to get the EXACT distance between the holes. as there isn't much "slop" to the fit. Also, you need to make sure that the holes are level. I'd use a long carpenter's level to pick the level off of the first hole to find the second one.
I also find it a good idea to drill a 1/16" pilot hole first, as it is always possible that the spot you picked is NOT between the studs. If you find that there is something behind the pilot hole (the drill will not continue to cut after about 1/2"), then you can use an ordinary wood screw instead of the moly bolt.
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This is all very good information - no wonder your a 'professor'. Thanks a bunch - makes my life so much easier!

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I hate those shelves. May the guy who designed them spend eternity installing them.
Your best bet is to use a screw 1.5" long the head of which will fit into the keyhole. If you hit the lathe behind the plaster you are all set. Second best choice is to use the long range molly. The sld above. PRE-drill the hole. Those are designed to hammer into drywall not plaster.
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I wouldn't hammer anything on a wood lath/plaster wall. Drill a lead hole for the normal screw and hope you hit wood lath. If not, get Mollies for thick walls, run them in to tighten, and back out for your shelf.
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Sue wrote:

I would mount a block of wood to the wall using mollies. Then user wood screws to mount the shelf brackets. You will have to control the depth of screws that the shelf bracket keyholes will go over[ which is impossible with mollies.
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