IF these are what I think they are, remembering different people call different things by different names.
Bullets are available in male & female and are just like spade connectors.
Often used on automotive applications.
Always put the female on the "live" side.
Not keen on them personally for mains voltage.
They are available in 3, 4, 5 & 6mm diameter bullets, in red, blue & yellow sizes from various suppliers, not all sizes are available everywhere.
There may even be some other intermediate sizes.
Are these the sort of thing you are on about because these are what I call bullet connectors.
I used red bullet connectors on Sunday when I took my exhaust off to weld up. The oxygen sensor in the exhaust was part of the exhaust so I had to cut the 3 wires going to sensor. Then reconnected them using male and female bullet connectors then wrapped in all up in self amalgamating tape. Job done. Was thinking of using wagos n a wagobox lol (joke).
Can these be used on mains voltage? The straight through ones Are ok so why not these ?
I call them bootlace ferrules , ZeeZee , usually for control cables , makes it easy to disconnect and re-connect without damage to cores and no stray strands . Panel work.