Spare & Replacement Parts by ECOTRIC. Details:The mechanical thumb for a backhoe attaches to the boom and has 5 possible positions to help you stabilize materials which are hard to control. Simply fold it back or slide out of the way when not in use. Hands down the easiest way to upgrade your backhoe. A mismatched thumb will result in damage to your backhoe, as larger backhoes have more bucket force. For example: if you mount a 25 thumb on a hoe that requires a 31 one, you will probably bend or break your equipment.