34 of the tool head 33 seats over the ribbed upper end of the cap 1 a set of six radially inwardly projecting splines 36 a f provided on the head 33 within the socket 34 are adapted to co operatively engage with the six splines 19 of the cap 1 when the tool 30 is turned about its longitudinal axis in the cap unscrewing direction the radially inwardly projecting splines 36 of the tool head 33 are of substantially uniform substantially rectangular cross section for much of their length but at their lowermost ends each is recessed with an arcuate recess cut out 37 referring to fig5 to 10 it will be seen that in the cap 6 in the short substantially smooth circular cylindrical portion immediately beneath the splines 19 there are formed two arcuate bulges 38 whose arcuate form is of a complementary shape to the arcuate recesses 37 in the splines 36 of the head 33 of the manual de capping tool the pair of radially outwardly extending protrusions bulges 38 on the cap 6 just below the splines 19 are substantially radially opposite to each other and partially radially overlap or are slightly offset radially from the immediately adjacent splines 19 when the head 33 of the manual de capping tool is passed down over the screw cap 6 and with the splines 36 of the tool 39 s head 33 interdigitating with the splines 19 of the cap 6 the initial act of beginning to turn the tool about its axis will cause the splines 36 of.