Wherever very thick walls (e.g. in the base area of a castle wall), natural rock or embankments are to be secured against drifting apart or slipping, very deep (sometimes several metres) round holes are drilled into them with special drills. There the so-called needle anchors are glued in. Needle anchors combine the properties of tensile strength and reinforcement. They consist of a profiled bar profile (needle), which has a holding or support plate on one side only. As a rule, the profile is a profiled round steel (e.g. ribbed reinforcing steel, threaded rod), which is pressed into the drill hole with mortar or adhesive.
The head plate or an anchor cross is mostly screwed on, so that after the setting process a pre-tension can still be applied by tightening a nut.
The MODERSOHN company produces needle anchors in various lengths and cross-sections.