I have come across a few of these objects in various places on these moors (NS4660 : Gleniffer Braes Country Park, NS4560 : Standing stones at Gleniffer Braes, and various others, whose photographs I have not submitted). For their dimensions, see the first of the links just given; they are much smaller than a trig point, for example.
In the present picture, a couple of NS4759 : Old gateposts serve as an identifiable background feature.