Press fit

An interference fit, also known as a press fit, is a fastening between two parts which is achieved by friction after the parts are pushed together, rather than by any other means of fastening. For metal parts in particular, the friction that holds the parts together is often greatly increased by compression of one part against the other, which relies on the tensile and compressive strengths of the materials the parts are made from. Typical examples of interference fits are the press fitting of shafts into bearings or bearings into their housings and the attachment of watertight connectors to cables. An interference fit also results when pipe fittings are assembled and tightened.

Gap Thickness
For different kinds of material there are different kinds of thicknesses for the gaps of you want to make a press fit. Here is a simple guideline for the materials used at FabLab:

4mm Wood - 3.5mm gap 3mm Plexiglass - 2.6mm gap 2mm Cardboard - 1.8mm gap