G17 Gen 3, 4, 5:
Mags
inner barrels
hop rubbers
hop tensioners (ML I-Bar)
G17 Gen4, 5:
recoil springs
hop arm
G19 Gen3 and Gen4, G17 Gen5
Hop unit
That’s about it. Basically everything else in the Gen5 is different. Even the pins in the hammer mechanism are different.