Two simple steps transform a mini engine into a standard size. Insert a mini engine into the adapter, and insert the adapter into a rocket. 3 adapters per pack. Reusable.
2316 – Engine Adapters Mini to Standard Description

Adapts standard engine mounts to hold a mini engine.

NOTE: Rockets weighing up to 2 ounces that would normally fly on A8-3 engines can be flown on A10-3T engines.