A vertical joint system (10a) for a surface covering panel P having an upper and lower surfaces (16, 18) a plurality of sides (20, 22, 24, 26) located between the upper and lower surfaces. The joint system (10a) has a male part (12) along at least one side (20) and a female part (14) along an opposite side (14). The female part (14) has a protrusion (54) that extends from the lower surface (18) and an outer most female surface (72) on the protrusion (54). The male part (12) has a recess (30) that opens onto the lower surface (18) with a portion of the recess (18) forming an inner most male surface (40). The outer most female surface (72) and the inner most male surface (40) arranged so that when the male part (12) of one surface covering panel is engaged with a female part (14) of a second surface covering panel the outer most female surface (72) overlies the inner most male locking surface (40) at a first location L1 and a second location L2. Datum surfaces (34, 62) are also provided on the male and female parts respectively that are pressed when the male and female parts contact at the location L1. This acts as a clasp to hold the male and female parts together, resisting vertical separation.