This is only for the Commercial THD range of Power Planters as they have a hollow tube where you insert this adaptor to use it on a regular drill chuck. 
H metal adaptor (ie to make it fit into a 13mm drill chuck)

When purchasing a Power Planter
428THD
528THD
728THD
you will need to also purchase this adapter if you have a regular 13mm chuck drill.
Or if you have a Petrol drill you will instead need T metal adaptor

On the NON-THD units (428H, 528H, 728H) the part that can get damaged over time is the hex end that goes in the drill. Rather than replacing the whole Power Planter, on the THD models you can just buy a replacement adaptor. 

The rest of the Power Planter range do NOT need this adaptor

Search Phrases: Power Planter Hex Metal Adaptor