|The following is based on Fallout Shelter and some details might contradict canon.|
The number of HP points gained per level up is tied directly to a dweller's Endurance level. With this knowledge, the maximum possible HP can be achieved on a dweller by equipping this gear on them at level 1 and with 10 Endurance (17 Endurance total) and then leveling them all the way up to 50.
|Wasteland gear||+3 Endurance||10||common|
|Sturdy wasteland gear||+5 Endurance||100||rare|
|Heavy wasteland gear||+7 Endurance||500||legendary|
Yao guai hide (3)
Chemistry flask (2)
Heavy wasteland gear (1)