Construction key is made of zinc alloy, rust-proof and durable, with laser-etched scales on the surface for clear, wear‑resistant readings. Back auxiliary scale: On the reverse side of the square wrench, measures cylinder lengths from 22 to 75 mm for quick sizing. Locking and keys: Includes a locking cylinder lock plate for pin lock; the housing structure is not built for a special lock cylinder. Comes with three square keys in sizes 6, 7 and 8 mm for checking heating valves or opening ventilation grilles. Top end and door work: The top end features a 3 mm Allen key and a short gear with a flat cam for loosening or tightening door handles. Use scenarios: - HVAC and ventilation maintenance: verify cylinder lengths with the 22-75 mm scale and use 6/7/8 mm keys to operate heating valves or open ventilation grilles. - Door and fixture servicing: loosen or tighten door handles with the 3 mm Allen key and flat cam. - General repair kits: rely on the durable zinc alloy construction and clear scales for frequent measurement and valve access tasks.