[paulengr]

Those are called ferrules, there's a lot of varieties out there. You'll want something UL listed, be careful when shopping, lots are not intended for line voltages.

Now that I think of it you'll want to be very careful the lugs allow ferrules, if they say "copper wire only" you might not want to use ferrules.

https://www.ilsco.com/Ilsco/ccrz__ProductDetails?sku=ACO-250-ILSM-ILS&cclcl=en_US

Example of aluminum to copper pigtail adapter.

Ferrules have the advantage that you have much less chance of loose strands and repeated connection/disconnection does not birds nest the ends. The disadvantage is more cost and time, and as mentioned compatibility. It’s hard to improve on copper and aluminum wire.