Confirmat screws or cabinet-connecting screws[1] are screws designed to hold in particleboard, medium-density fiberboard, and similar materials. They are very common in furniture assembly, but are rare in retail.[2] They may have flat or barrel heads. They have a blunt tip, a large shank, and they often have shoulder, a broad length of unthreaded shank just below the head, which helps hold the screw in position.[2] They have a coarse thread, rather like masonry screws (which may match them exactly in thread).
Confirmat screws are usually screwed into stepped predrilled holes,[3] often drilled with a stepped bit.[2] Short, shoulderless confirmat screws, whose heads pass through hardware like hinges or drawer slides, may go into unstepped holes.[2]
As they are screwed in, confirmat screws compress a thread (the spiral groove) into the particle board. They do not cut a new thread if removed and re-inserted. A confirmat screw can therefore be removed and replaced dozens of times.[4] However, a confirmat screw can not be replaced by a confirmat screw with a different thread, or it will destroy the threading of the hole (filling the hole with a wooden dowel and using a woodscrew can fix a stripped hole[2]).
Confirmats may be made of steel, galvanised steel, and nickel and aluminium-zinc alloys.[5] They commonly come in lengths of 40,, and in shank sizes of 5,, with Phillips drive or hex heads.[4]
Ordinary wood screws do not hold well in particleboard, which is much weaker than wood. They tend to tear out.[6] Confirmat screws have about twice the shank diameter of a woodscrew. Drywall screws, while half the price of confirmat screws, do not hold as well in particleboard-like materials, and cannot be removed and re-inserted. Cam-and-bolt connectors can be swapped out, but are more complex and expensive;[4] confirmat manufacturers say they cams are also weaker than confirmats, if better than drywall screws.[4]
Confirmat screws were formerly under patent, but the patent has expired, and they are now made by many companies.[4]
The name comes from the Latin word confirmat, meaning "it makes [something] firm or strong".[2]