start off with your weights (in this case I used 1,2,3 oz), some alligator clips (Lowes electrical) assorted shrink tubbing (Lowes electrical) and some large spilt rings.
Step 1. trim alligator clips back so that the whole for the wire is within a 1/4" of the end (this makes attaching the split ring possible), I used my dremel with a cutting disk for this.
Step 2. attach the weight and the alligator clips with a split ring (I found that its easiest to get the ring started on the weight; and put the weight and alligator clip side be side and twist it on the two and the same time with a pair of needle nose pliers)
Step 3. Starting with the smallest shrink tube that will fit over the jaws of the alligator clip, cut and heat with a lighter to shrink on to grips. apply 2-3 layers of shrink tubbing, heating each layer before the next is attached (tip: dip the alligator clips in water before you close them so the hot shrink tubbing doesn't stick together)
Finished snap weights.
Now you can figure that a 1oz snap weight will get you down about 10ft, a 2oz about 18ft and a 3oz about 22ft.. at 2mph.. now for every 1/10 mph over 2mph you can subtract about 1 foot of depth and for about every 1/10 mph below 2mph you can add 1 foot of depth...this is figuring a 50/50 method (50 feet of line to snap weight then 50 feet of line to rod)
One other way they I like to utilize snap weight is if you are getting a hot rigger bite in shallow water (I only have 2 riggers on my boat, so lets say that they are being run down 4 over 12 fow and back 100ft) I will let out the desired lead, put a 3oz or 4oz snap weight on the line, then place the rod in a holder at a 90 degrees to the boat. I will the let out line with the rod in the holder until the snap weight is down 4 feet. In shallow water this doesnt take much line and you can usually see the snap weight. giving you a sort of poor mans outrigger, giving me 2 down riggers and 2 out riggers.
By the way the 6 snap weight i just made cost around 6 bucks to make. compare that with the 8 or so offshore is getting for one 3oz snap weight.
Tight Lines!