Door Knob Locks and Concealed Door Locks: Cases, Backsets and Sizes

Updated 2026-11-08 · RAYEN 雷茵

A knob suits a door where a lever would catch clothing or look too heavy: a wardrobe, a hidden door flush with the wall, a quiet bedroom. Our knob locks sit in the lever handles range, and they differ more in the lock behind them than in the knob you see.

Which knob locks fit a mortise lock case?

• KA5-A011 and KA5-A012 work with lock case 8550 / 7255, on an Ø52mm rose, for 38-50mm doors. The keyhole has its own cover, as the photos show. KA5-A011 has a leather-wrapped body; KA5-A012 is plain metal with a ribbed band.
• ET4017 uses a CF60 lift-to-lock case, an Ø55mm rose and a 50mm projection, for 40-58mm doors. The photo shows a ribbed cylindrical knob with the fixing parts running between the two halves.

Our guide to lock case numbers explains 8550, 7255 and CF60.

What is a concealed door lock?

A concealed door lock is made for a hidden door: a leaf finished flush with the wall, where the hardware must stay small. It uses its own compact lock case instead of a standard mortise case.

• A5-A002: lock case K58, backset 58mm, face plate 23 × 78mm, Ø54mm rose, 58mm projection, for 38-50mm doors. The photos show an oval knob on a round rose, and the lock body behind it. Finishes: matt black, antique bronze and zirconium gold.
• A9-987 BL: lock case K55F, for 38-50mm doors, in matt black. It is a lever, not a knob: a thin square-rose lever with a thumb turn, and the photos show a separate cylinder and keys.

The K codes do not follow the four-digit rule of standard cases. On A5-A002 the 58 is the backset, measured from the door edge. Take the figures for A9-987 BL from its own drawing.

What about the knob pairs without a lock?

We also list knob pairs on their own: A5-A008 and A5-A009 with round faces, A9-A010 with a square face, A5-A011 with a leather-wrapped body and A5-A012 with a ribbed body. Their finishes are listed; their sizes and the lock they pair with are not yet on the page. Ask us for the drawing and say which lock case you plan to use.

Is a cylindrical knob lock the same thing?

No. KQ101 SS is a cylindrical lock: a round chassis sits in a bored hole between the two knobs, with a latch in the door edge. It needs no mortise pocket. For bored-hole locks with levers, read tubular lever lock backset.

How do you choose between them?

• A standard interior door with a mortise lock, or a new door: a knob set on 8550 / 7255, such as KA5-A011.
• A thicker door, up to 58mm: ET4017, which lists 40-58mm.
• A hidden door finished flush with the wall: a concealed door lock. Check the door edge has room for a 23mm-wide face plate on A5-A002.
• A door already bored for a bored-hole lock: a cylindrical knob lock such as KQ101 SS.

What should you measure?

• Door thickness at the lock, on the finished door.
• On a hidden door, the width of the door edge and the depth available behind the facing.
• On an existing lock, the backset and centre distance, and the face plate size.
• The gap behind the door. A knob needs room for the hand; A5-A002 stands 58mm off the door.

What to write on your order

Write the model, the lock case, the finish and the door thickness, and say how the door is used. For example: A5-A002, lock case K58, backset 58mm, matt black, hidden door, with your measured door thickness. Or KA5-A011, lock case 7255, matt black / brown leather, door 38-50mm. If the door needs a key on one side and a turn on the other, say so on the line, and we will confirm the lock that does it.

Open the selection tool：Lever Handle Finder by Door Thickness and Lock Case→