These are also referred to as diff joints or diff cups

Traxxas XL-2

it fits perfectly with the stock transmission components and installs with basic hand tools

The Losi LOS252066 Diff / Differential Housing Set Aluminum (1) Desert Buggy XL-E is a genuine Losi replacement part identified by part number LOS252066

and 4x14mm BCS hardware (4)

Losi LOS252061 Center Diff / Differential Spur Gear 48T / 48Tooth Mod1.5 DBXL-E servo These are also referred toLosi LOS252061 Center Diff Differential Spur Gear 48T 48Tooth Mod1. 5 DBXL E This LOS252061 spur gear is a genuine Losi center differential gear cut with 48 teeth in Mod 1. 5 pitch, built as a factory matched replacement for the DBXL E. Genuine Losi part LOS252061 Center differential spur gear 48 tooth count Mod 1. 5 gear pitch Fits the DBXL E