Prescott Plastics high quality high grade plastic plug. These end caps work with round piping with an OUTSIDE DIAMETER of 1 1/2". *PLEASE NOTE :: These do not fit 1.5" HOLES. Please select 1.75" size for 1.5" holes* These fit round tubing with INSIDE DIAMETERS (ID) of 1.25" to 1.43" (1 1/4" to 1 7/16"). Our heavy duty plastic plugs are manufactured to provide a secure fit on multiple tube gauges.