VEVOR 3-Stage Hand Stirrup Pump Stirrup Pump 4500 psi (0-30 MPa) Air Gun Rifle Pump Filling Stirrup Charger PCP Hand Pump Airguns with High grade 301 stainless steel

I recieved my pump today,and not sure if ive assembled it correctly as the instructions are not very clear.how far do i insert the preasure gauge as it wont screw in all the way down the threads.and is that bag of seals just for spares or do i have to put them in the pump before i use it? Any help would be greatfully accepted.