Hook: Floor Medium (Blue Square)The Generator (Blue) decoration fits into a blue medium square floor hook.
Hook: Floor Large (Purple Square)The Generator (Blue) decoration fits into a large purple square floor hook.
How to Get a Generator (Blue) Decoration
Cartel Pack Decorations
The Generator (Blue) decoration can be dropped from GEMINI Alliance Packs, which were released on the Cartel Market and bought with Cartel Coins. Cartel Packs, including the GEMINI Alliance Pack, include a random selection of items from the GEMINI Alliance collection of items. You aren't guaranteed to get a Generator (Blue) decoration from a GEMINI Alliance Pack, but it is one of the few ways to get a Generator (Blue) deco apart from buying it on the GTN from another player.
If you're looking to get a Generator (Blue), the easiest way to get it is to head to the Galactic Trade Network (GTN) in SWTOR and buy it with credits from another player. If it's very rare and not available on the Cartel Market, you could try buying from the GTN and hope you get it.