The Magnum Lift LEGB-2 and Barker PowerPac 12 volt electric powered motor conversion kits for 2 speed landing gear jacks are designed to mount to a 1-1/2" diameter collar (support hub) welded to the outside of the formed steel gearbox body.
This hub would normally be on the lower (crank) shaft of the jack gear box.
Holland/Binkley brand jacks manufactured after September 2010 no longer have the external support hub welded to the gear box.
If this hub is not present on your jack you will need to purchase this 1-1/2" Support Hub Bracket kit.
The adapter kit is designed to bolt to the jack gear box utilizing 3 of the existing gearbox cover attachment holes.
The required bolts and spacers for hub adapter attachment are supplied.
See the jack image above with the support hub circled for clarification.