They are one part of a number of classic theater type hardware used for joining soft flats together on
stage in a way that the flats are really easy to remove for scene changes. Or for in the days before drywall screws and even double headed nails.
Basically they are put on opposing inside edges of soft flats and a rope hanging from a wise eye
cleat at the top is run between the lash
line cleats as if a zipper in joining the flats together. Takes but a second to remove the rope joining the scenery. Backstage handbook shows a type of slip knot used at the bottom of the
flat in terminating it. Old books on stagecraft show how this type of thing was done.
Lash cleats, stop cleats, tie off cleats and or
flat lash
line cleats between the flats help hold the flats flush and parallel. The most difficult part short of using the lash
line concept is in joining the flats initially thus the various even angle irons and various plates between flats to make the flats parallel. Than in holding up the
flat and keeping it in place... wailers with keeper hooks, brace cleats, bent brace cleats,
stage braces,
stage jacks, or tip jacks, and
stage screws at times.
Did the lash
line concept before... easy to remove somewhat difficult to install and get tight enough. This especially if you can't do the
stage brace/
stage screw concept. Most theaters these days froun upon
stage screws into the floor. Drywall screws are at times permissible but take time. Sand bags at the rear of a
flat only work to an extent in keeping the scenery put at the
base. For the upper part of it, while you can do a rubber bottom
boom base a plywood plate that's sand bagged, it's difficult to get enough weight there quickly enough, much less remove it fast. Better yet use hinged to the scenery
stage jacks that are
stage weighted by extra weights for the fly
system, it takes extra effort and time to remove the weights but the
stage brace supports both the scenery in it's height and the bottom of the
flat. This much less a good
stage brace wouldn't be cheap but a
stage jack would be a few dollars worth of 1x4 and plywood.
Such hardware all above is also useful for other things...