The options in the drop down menu are telling you exactly what joint size/type is on the adapter.
For example:
1. "Double Female - 10/14MM"  This literally means there is (1) 10MM Female and (1) 14MM Female fitting
2. "14MM (Female) to 18MM (Male)" This literally means there is (1) 14MM Female and (1) 18MM Male fitting

Common scenario.
1. You want to buy a drop down adapter that keeps your rigs original joint type the same.
- So if your rig is a 14MM Female and you want to keep 14MM Female then the correct choice would be the "14MM Male to 14MM Female" option.

2. Also keep in mind that "14MM Male to 14MM Female" is the same as "14MM Female to 14MM Male"

**Beginners Info**

- Male fittings fit into Female fittings
- Female fittings fit onto Male fittings
Examples:
1. Rig Joint has 14MM Female, this means you need a 14MM Male fitting to fit.
2. Rig Joint has 14MM Male, this means you need a 14MM Female fitting to fit.