Ideal Electrical Wire-Nut® (30-172P) Wire Connector, Model 72B® Blue, 100/Bag

I use Ideal brand wire nuts because I know what I’ll get when grabbing blue, yellow, grey or red ones from my bins. Size of the spiral wire inserts vary across brands so you don’t always know if the size you’re reaching for will be as expected based solely on color and shape. There are usually multiple sizes that work for a given wire combo connection, but there’s always an optimum size so I carry all of them since I connect a variety of wires doing HVAC work. These blue ones are perfect for 2 18 gauge low voltage, stranded wires . The grey ones will work but are a little short. The orange ones work but the extra size can mean the bundle of wires are too tightly crammed into an enclosure. Depending on the specific connection I like having choices handy and the quality has been consistent over the years.

These are just a bit more expensive than the no name ones, but once you have to remove a wirenut and the threads stay on the wires, you will never buy the no name nuts again.