Very happy with the choice of these attachments. Sizes fit most bulkheads, make sure you order bulkheads first to ensure they fit the hole you are drilling. Tip: Create a block template to hold the drill securely. The picket fence is the perfect size, simply cut it to size. Now drill a hole (use a wood drill bit). This block does several things. It prevents the drill bit from slipping on the glass, gives you a grip, protects the glass from drill bit strikes, provides a "pool" for cooling water, and protects you by protecting your hands. Use water to cool and lubricate the glass. a little. It's not necessary, but it helps. Your block of wood will hold water, just add it every few seconds. Push carefully. Take your time slowly and safely. The block of wood also gives you a chance to line up as your drill bit will hide where you marked the hole you want. Simply measure the distance from the edge of the glass to the edge of the block of wood. Know your hole center, yes! Well positioned hole. I was making a terrarium but wanted my water feature to be about 4 inches deep. So the bottom hole (in the attached photos) is for draining. I adjust the height by turning the overflow strainer at an angle until I get the correct water depth. I can increase the water depth by adding a riser, but there will always be at least 3 inches of water. My income is high because a waterfall feature is planned.