I've been converting my old T12 fluorescent fixtures to LED. Rather than mess with the 30 year old tombstones it's easier to rip everything out and replace with new. These are nice as they "clip" in place and don't fall off of the bracket. I tried to use the ones that came with the LED's as a kit but they were horrible. I spent more time fumbling with them because they would not stay on the bracket, than the entire retrofit of the fixture. These are priced so I don't mind tossing the ones in the kit! It's amazing what a simple thing like clipping in place means when you are up on a ladder with your hands over your head!!

These are just okay. They don't hold the wires in place very well. While you're installing them (if you've already pushed the wires into the holders, the wires have a tendency to fall out if you're not extremely careful. Once installed and not touching or moving the wires, they work fine. Just be cautious about the wires losing continuity if you're not extremely careful when inserting the wires or if you're moving the wires to hide them once they're installed.

Seem well built. Grab wires well when inserted.

They are correctly advertised as T8 holders. No problem.

Just an FYI note...
T8 holders are shorter than T12 holders. However, from my experience, they also work with T12 bulbs in most cases. They fit T12 bulb pins, and are long enough for the typical fixtures I have placed them in. However, I had a few fixtures that had the sockets recessed an unusual amount since they did not use the typical standard mounting slots. For those, a true longer T12 socket with the other mounting type would have been better. (Not the fault of these sockets of course. I just used what I had as long as it was safe.)

These are a great deal if you need several. If you try to buy them at home Depot or Lowe's you will pay this much for four of them.
I needed these for standard T8 bulbs. Since these are Non-shunted I had to use a short piece of 14g solid insulated wire to make them shunted. What the jumper does is electrically connect the metal prong on one side of the tombstone with the other metal prong on the same tombstone. The piece I used was probably 6" and I stripped 1/2" off both ends, bent it into a tight U shape and inserted it in the middle two holes below where the bulb connects. There are four holes total. The others are for the ballast and to connect them together for the amount of bulbs your ballast is made for. Make sure you follow the wiring instructions on the ballast. It's not hard. I suggest adding the jumpers before you put the tombstone in place.
I used these to make a rack of t8 bulbs for starting seeds for our garden. No need to buy the light fixtures, just buy these, ballasts, some drywall screws, wire nuts, electrical tape, wire stripper and an inexpensive household extension cord for power by cutting and splicing the ballast power wires to it.

I actually used these in a way that JackyLED probably did not intend or endorse, but for my purposes, they worked perfectly. I directly wired these to 120VAC, screwed them to my basement ceiling, and popped in T8 Led bulbs (powered from a single end). Each "fixture only ended up costing me around $8 and they look sleek and minimal.