Modular valve with blind plug

[isr_tt89]

Hello.

I just purchased 2 80cf Al tanks and modular valves with blind plugs.
I need to assemble them.

San-o-sub valves
San-o-sub plugs

Left and right valve.
When I tread in the plug, it will not go all the way in.
There is about 1 mm gap between the nut and the valve's surface. The other valve's plug goes almost all the way to the end.

I have measured depth of the hole in the valve and its about 35 mm.
The plug is about 33 mm long (untill the nut).

I also measured the thread portion of the valve hole and it is longer than the plug thread (until the nut).

I am trouble understanding why it will not go in all the way - all I can think of is that the valve hole's bottom part is tapered.
The valve link also includes a link to the manual of the valve but it does not help me.

Do they have to go all the way in - the sealing surface is where the O-rings are ?

Any ideas ?

Also, anyone has torque spec for the plug ?
Do I need to lubricate the 2 O-rings on the plug like the M25 thread on the valve ?

Thanks in advance!

PS! English isnt my first language.

 

[runsongas]

a small gap is acceptable as there is plenty of tolerance. they aren't face sealing so the orings do not have to be flush, just within the stem far enough.