What is a mortise lock?

A mortise lock is a reliable guardian of your door — especially relevant in Ukraine, where according to the National Police around 50,000 thefts are registered annually and approximately 40% of them occur through insufficiently secured doors. What is a mortise lock? It is a mechanism installed inside the door leaf, protected from view and direct impact. It combines security classes 3–4, aesthetic integration, and a service life of up to 25 years.

Unlike surface-mounted solutions, these systems do not deform. Standards define their technical parameters, and selecting the correct size according to door dimensions is essential. The price depends on the material and the complexity of the mechanism. Installation requires professional skills but ensures reliable protection.

What does backset mean in a mortise lock — full description and characteristics

The term “backset” refers to a key parameter — the distance from the faceplate (front edge) to the center of the handle or cylinder opening. This value typically ranges between 30 and 85 mm. It determines compatibility with the door — 60 mm is considered the standard size for most applications. Without the correct backset, proper installation is impossible.

Detailed technical characteristics:

• Housing. Made of cast steel or brass; galvanized surfaces provide corrosion protection — important for the local climate.

• Bolts and locking elements. 4–8 steel bolts and beveled latches for self-closing doors.

• Faceplate. Length 240–320 mm, with cutouts for the strike plate.

• Cylinder mechanism. 6–12 pins, protection against bumping, picking, and drilling.

• Handle connection. Thumb turn (“butterfly”) or torsion mechanism; square spindle 7–8 mm, axis diameter 18–22 mm.

• Weight and dimensions. Weight 1.8–4 kg; height 120–280 mm, width 55–80 mm.

• Security level. 10,000 to 1 million combinations; key duplication often possible only by the manufacturer.

• Fittings. Stainless steel AISI 304; finishes in chrome or nickel.

• Load resistance. Up to 500 kg door pressure — suitable for steel entrance doors.

• Climate resistance. Temperature range from -40 °C to +60 °C, humidity up to 95%.

• Certification. Confirmed by passed tests in accordance with applicable standards.

This information helps realistically assess product characteristics before purchase.

How to measure a mortise lock correctly to ensure proper operation

For accurate selection, it is recommended to use a measuring template. The faceplate, backset, and milling depth must be measured. How does a mortise lock work? The key turns the cylinder, which transfers force via a gear to the locking bolts. Left-hand (counterclockwise) or right-hand (clockwise) operation depends on the door swing direction.

Step-by-step procedure:

• Preparation and measurement. Use a caliper to determine faceplate height (e.g., 250 mm) and backset (e.g., 60 mm).

• Milling depth. 35–55 mm; cutter diameter approximately 50 mm.

• Cylinder spacing. Distance between openings 70–120 mm.

• Handle spindle. Square 7–8 mm, axis diameter about 20 mm.

• Operating principle. The key aligns the pins, unlocks the rotor, and the gear moves the bolts.

• Thumb turn mechanism. 90° rotation without a key for the latch.

• Electronic version. RFID chip with motor drive; automatic locking after 30 seconds.

• Installation. Requires template, angle grinder, and appropriate drill bits.

• Fastening. M8 screws (4–6 pieces) and sealant if installed in wooden doors.

• Testing. Check at least 100 locking cycles; bolt adjustment ±2 mm.

• Lubrication. Use graphite or silicone spray; do not use oil.

• Common mistakes. Incorrect left/right selection or looseness due to insufficiently tightened screws.

• Compatibility. Door thickness 35–120 mm — optimal range.

Measurements should always be taken twice to ensure accuracy. Proper installation accounts for about 80% of success. A mortise lock is considered an optimal solution for residential properties — reliable, concealed, and universally applicable. Carefully verify the backset, dimensions, and door swing direction. For maximum security and durability, installation by a qualified specialist is recommended.