The o-ring belts are an excellent choice to replace OEM v-belts. They are more elastic and will outlast the original OEM belts. Compatible with both single and dual drum tumblers manufactured under the names Chicago Electric and Harbor Freight. Also compatible with Lortone 33B & 45C. Note: if you are experiencing a high usage of belts, check your pulleys for burrs or rough edges, this may contribute to premature belt failure. Outside diameter is 3-7/8″.