APC-Landing Products Adapter Rings 6 Sets (1/8", 4mm, 5mm, 6mm, 5/16") These are the APC Propellers Adapter Rings for Thin Electric Props.Features:Grey coloredAllows props to be used on a variety of motor shafts and gear drive systems Includes:Six of the following Adapter Rings; 8mm inner diameter 3mm thick 5mm inner diameter, 3mm thick