The options in the drop down menu are telling you exactly what joint size/type is on the adapter.
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
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"
¬†- Male fittings fit into Female fittings
¬†- Female fittings fit onto Male fittings
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.¬†