Armour ability problems.

[Seth Keidashi]

Okay. So I was wondering something about FFX.
When customizing armour, if you have the required items, the ability should show up right?
Well. I looked on an online guide how to put "Master Thief" and "Auto-Haste" and all that fancy abilities, and gathered up the items.
Problem.
I have all 30 of the "Pendulum" items needed to get master thief according to the guide. (I got them by opening 4 chests during the chocobo race at remiem temple.)
But the ability still isn't showing up.
It's not grayed out.
It's just not there period.
Is there something I need to do before some of the special abilites are available? And if so, what??

*NOTE* Problem solved. I was stupid enough not to realize I was trying to customize on of rikkus WEAPONS and not an armor.