An electric hair clipper (8) comprising a first clipper body (10) having a support tongue (34) pivotally mounted on an inclined front end (9) of the clipper body (10), the support tongue (34) having an upper surface (35) opposing the inclined front end (9) and a top end (36); a first cutting head assembly (12) releasably and operably engageable with the first clipper body (10), the first cutting head assembly (12) having a tongue-receiving socket (42) for releasably receiving the support tongue (34) and comprising a strap (40) disposed on a bottom blade (14) of the cutting head assembly (12), the strap (40) having a central portion (43) with a bottom end (48) and an inner surface (47) opposing the bottom blade (14); and a first projection (50) disposed on the upper surface (36) of the support tongue (34), a first slot (44) having an open end (44a) defined by the bottom end (48) of the central portion (43) of the strap (40), a second projection (52) disposed on the inner surface (47) of the central portion (43) of the strap (40), and a second slot (46) having an open end (46a) defined by the top end (36) of the support tongue (34) wherein the first and second projections (50, 52) are received in the first and second slots (44, 46), respectively, when the support tongue (34) is inserted into the tongue-receiving socket (42) to releasably and operably engage the first cutting head assembly (12) with the first clipper body (10) and also to prevent the first clipper body (10) and the first cutting head assembly (12) from being releasably and operably engaged with other cutting head assemblies and clipper bodies, respectively.