1. Applicable materials. Our shower door pulleys are made of galvanized plastic alloy, so you don't have to worry about rust. On the other hand, plastic alloy greatly reduces the risk of glass breakage due toto collision while ensuring the slip resistance of the shower door pulleys. 2. Copper swing and stainless steel screws should make the product more durable.Rolled on top, these shower door rollers fit 4-6mm glass thickness and 13.5-14mm glass openings, 23mm wheel diameter and feature 4 blocksAdditional bumpers to best protect your shower door. 3. Adjust the height of the glass with screws.There are rollers at the bottom, and the height of the lower wheel is adjusted according to the upper wheel. 4. Glass hole 13.5-14mm, due to manufacturing reasons, there may be 0.5-1mm error, but the common glass hole for most of our shower door rollers isfrom 13.5 to 14 mm.If you are unsure of the size of the glass opening, it is recommended to measure the diameter manually in two steps. 5. The adjustment range of the upper wheel is 8mm.Turn the screw at the top to adjust the height of the wheel.Once tightened (the wheel no longer goes up or down), this is the maximum adjustable height, please do not overtighten to avoid any damage ​