So to those of you that never used a slot extender I will make a little guide for you.

Extending.
Extending an item gives it an extra slot to fill it up with an upgrade and it becomes account bound. Slot extenders don't fail don't worry about that. Just right click the extender and click your item to extend it.

Extending bonuses.
Ok, so when you extend an item it gives you some bonuses for most enchants here's a list of them.Great sword/dk values are doubled.(Only posting the ones I think are useful Idgaf about the others.)

S.amp/M.amp 7% -------------------------->No bonus
Hp -------------------------------------------->First hp slot gets turns into 80 hp rest are 50
Attack/Magic attack ------------------------> Slots turn into 5attack/M. attk
Crit Damage ---------------------------------->This one is wierd damage is capped at 25% and slots become 12% each.
Example: You extend a blade with 20% damage and want to fill it up with another crit dmg slot it would go[12][12][1].
Crit rate---------------------------------------->Turns to 7 rate
Max crit rate---------------------------------->Turns into 3% max rate
Hp steal----------------------------------------Turns into 3%hp steal
2slot item drop-------------------------------->300% 2slot item drop

Dextending, upgrading +8-+12
To dextend an item or upgrade it you go to the core alchemist and item upgrade it(must be +7.)

Then if you fail and receive a penalty the item goes back to +0 dextended. So if you're upgrading don't fail. If you have a lv2 enchant in the 2nd slot and you dextend it you lose the lv2 enchant.

Alright this guide may have errors, feel free to correct if you want/give suggestions idc. Idgaf if there's another extending guide I typed this already Kthxbai.