The biggest difference is the price $449 vs $695
First the STD (standard duty) a-arms, they were designed for the weekend warrior, the person who worked hard all week and wants to play hard on the weekends with the Toyota.
The HD (heavy duty) a-arms are for more extreme offroad abuse like offroad racing, extreme rock crawling and jumping dunes.
- a big difference is the price $449 vs $695 plus shipping
- the geometry is the same, they are welded on the same jigs
For more pictures and details go to https://jbaoffroad.com/trails/difference-between-jba-std-ucas-vs-jba-hd-toyota-ucas/
The JBA UCAs will give you 1" extra down travel on the front suspension with more ball joint travel and more a-arm to strut spring clearance.