This listing is for a pack of 4 TL431 (TL431A), in TO-92 Through Hole Transistor package. Each "item" you buy is 4 TL431 devices.
I expect you already know what a TL431 is if you are looking at this listing, so just google for datasheets and tutorials and so forth as you desire.
These parts are sourced from the usual no-name chinese vendors, exact manufacturer/specifications can not be relied upon, so yeah, don't use no-name chinese parts in critical applications, for hobbiests, no problem!
