The adjustable square slit ASR12 provided by LBTEK features an M4 threaded hole at the bottom for free-space applications. The slit is adjusted via a threaded mechanism with a range of 0–12 mm square. Each full rotation of the threaded mechanism corresponds to 0.5 mm, and bidirectional adjustment allows for any square dimension within the 0–12 mm range (controlled by four adjusters, each managing a slit blade with a 0–6 mm range; the combination of the four knobs enables any square size within 0–12 mm). When fully closed, the theoretical slit width is 0 mm, though machining and assembly tolerances may result in a maximum gap of 0.02–0.05 mm. The LBTEK adjustable slit is made of wear-resistant tool steel, treated with a black finish to minimize stray reflections. The mating edges are precision-ground to ensure flatness and burr-free performance. Notes: 1. If burrs or unevenness develop on the edges after prolonged use, gently wipe the edges with alcohol. 2. Adjust only within the specified range; excessive adjustment beyond the travel limit may cause the lead screw to detach.