Regular readers will know that I love the Wago lever nuts for making solid, reliable connections in domestic mains voltage wiring. But another connector I use a lot is the jelly crimp.
Jelly crimps are the mainstay of telecom installations and repair (at least here in the UK). I was introduced to them many moons ago by an engineer, and he gave me a handful, and ever since I've been hooked.
They come under lots of different names, from "jelly crimps," "gel crimps," "LJ8A," "LJ8B," or "Gel/Jelly Filled 8A Type Crimp Connectors," and they come in two-way or three-way configurations (depending on whether you want to connect two or three wires), and they have been specifically designed for joining solid core copper or aluminum telephone and communications wires.
They can take wire with insulation up to 2.06mm thick (which accommodates insulation that might be roughly cut and flattened at the ends), and the conductor size ranges from 0.4 to 0.9mm (26 to 19AWG).
Note: The ones I've found designated LJ8B, which seem to be an upgraded version in the UK, take wire 0.4 to 0.7mm.
The "jelly" bit in the name comes from the fact that the ends are packed with a dielectric sealant that both adds extra insulation and also makes the connection weatherproof.
They're dead easy to use.
You cut the cable, poke the ends in all the way (no need to strip the insulation), and squeeze the button to snap them down and bite through the cable.
Their primary use is on telephone wiring, but I've also used them on alarm systems, doorbells, speakers, and other low-voltage applications. The connections are highly reliable, and as long as they aren't submerged in water, they will last for decades (and even submerged ones have a long life, in my experience).
There is a special tool for doing the squeezing that you can pick up for $15, and if you do this a lot this might make sense, but I find I can use my finger and thumb, or a pair of Knipex mini waterpump pliers to do the job.
Did I mention that they are incredibly satisfying to "pop"?$18 at Amazon
These connectors can handle up to 50V, so don't use them on mains voltage or someone -- possibly you -- may die. I've also seen them used for network cable repairs, which I don't recommend (it's a terrible idea).
A pack of 100 3M jelly crimps will cost under $20, but if you have a lot of crimping to do, you can pick up a 1,000. You might be able to pick them up significantly cheaper from a trade outlet. You can also find cheaper, no-name brands but I find them to be variable. In the UK I tend to go for the DeX branded connectors because there are the ones used by the telecoms companies.