All of the accessories to get your scuba diving, freediving or spearfishing weight system fully sorted are available from The Scuba Doctor at everyday low prices.
Threading a 3-Slot Quick-Release Belt Buckle
Starting from the front of the metal buckle, thread the left waist strap through the larger end slot of the buckle. Position the buckle approximately 45 cm (18 inches) of webbing length from the plate left waist slot. Then thread the webbing from the back through the centre slot and through the front of the inner most slot. Then thread the webbing through the back of the larger end slot so there are two thicknesses of webbing through one slot and pull the weave tight.
Threading a 2-Slot Quick-Release Belt Buckle
While we don't recommend the use of 2-slot belt buckles, if it's all you have then this is the way to thread them.
See also, How to Thread a Weight Belt Buckle.