the slot 18 includes a raised mouth 20 a ceiling ramp 20 b and a forward stop 20 c the cartridge rack 14 is insertable into the base 12 by sliding the pins 16 into the mouths 20 a to the rear and slightly down when the cartridge rack 14 is drawn forward the forward motion is stopped when the pins 16 contact the forward stops 20 c the rear of the cartridge rack 14 may be raised to allow the pins 16 to clear the forward stops 20 c to remove the cartridge rack 14 from the base 12 a side view of a rear portion of the cartridge rack 14 is shown in fig1 when the magnets 22 a and 22 b are separated and the front of the cartridge rack 14 is lowered a stop angle s is provided by a sloped portion 24 at the extreme rear of the cartridge rack 14 rises against a ceiling or bottom face 26 of the base 12 preventing further tilting of the cartridge rack 14 beyond the angle s a side view of a rear portion of a two piece cartridge rack 14 a is shown in fig1 a the cartridge rack 14 a includes a metal.