White Finish Frameless Shower Door Half-Round Aluminum Threshold. The low profile contour shape is gentle on the feet while providing a good dam to allow water to drain back into the shower floor. It is normally mounted directly under the shower door but may be mounted slightly offset to the door to provide the right amount of seal for the door's bottom sweep. Easy to install using a bead of silicone sealant. 1/4" Height x 13/16" Wide. 36" Long.