Spanish to English Tech/Engineering Mechanics / Mech Engineering Lift contraption to assist people into and out of swimming pools

Hello,

I am translating part of a manual concerning a lift contraption that enables a person to lower into and out of swimming pools. The lift consists of a metal framework to which a seat is attached that can be raised and lowered. I'm afraid this file only has text and there aren't any diagrams to demonstrate what goes where. I'm after the sentence structure in English please for the following:

"Colocar a la baranda de apoyo (7) el brazo inferior en el casquillo previsto para tal fin". I have translated it as 'Position the lower arm to the support railing (7) in the cap provided for this purpose'.

Or, should it be 'Position the lower arm in the cap provided for this purpose to the support railing (7)'?

Thanks,
Salma