How to adjust shock preload?

[dhdallas]

These are Noleen NR-1 shocks on an old Girvin ProFlex MTB. How do I get a grip on the preload adjuster? There is very little surface area & there are no notches for a typical spanner & a pipe wrench, vice grips, etc. which are sure to mar the springs if I can even get them in there to grip it. The working space on the fork shock is especially tight. See attachment photos. Thanks!
   
   

[ReapThaWhirlwind]

You see that thread?

Screw that thread in (clockwise) to compress the shock and increase the pretension.