I’m trying to refurbish an old Trek mountain bike (volunteer community bike shop) and I want to service the RST fork.
I need to be able to remove the preload adjuster knobs but I do not have the RST special wrench PN #H5GAC616

as described in the manual I found.

Would you folks know if another tool or method that may work to remove those adjuster knobs please?

If you're careful a crescent wrench on the tab in the middle will do to loosen them, but they may break if the plastic is brittle - adjust the wrench tight, and push it down as you turn, hope it breaks loose without much force. Those forks weren't worth much before they got rusty, I'd be inclined to give the stanchions a scrub with oily wire wool, the legs a shot of oil, and chuck them back together. (I had some similar RSTs that weren't rusty, they did respond well to a clean and grease, but they were too flexy so I replaced them with a rigid fork).

that wrench is about $10 , delivered, and found easily on Ebayt or Amazone.. i've messed around trying to avoid buying one, in the distant past... just buy one.

search: RST fork cap wrench tool.... visually match an option to your fork's caps.

or get a new fork... that one might be beyond salvage/repair, eh?
good used air forks of a higher level, and Substantially Lighter weigh, are around for about $100-$150... FB marketplace and CL Bicycle parts section... and sometimes on Ebayt too.
install quite a few RockShox Rebas and Recons, and occasionally old SIDs too.
i found a nearly spotless Marzocchi Bomber Superfly once, for $25... perfect for my Cannondale M600 resto-mod.
patience and diligence is the key to finding bargains.

steerer tube length MUST be at least as long, or longer than, the fork now in the bike.
that bike uses a 1 1/8" dia. straight steerer tube.

Yes,I did find the tool, but it’ll be a while arriving and was curious about other options.

As to buying a new fork, I agree with what you typed. But I do enjoy bringing things back to life and it’s not like this bike will be used on technical trails - this is a community bike shop where we refurbish old bikes, with a low budget and I have to balance cost of the work or part. Besides, the place is an environmental and art learning centre and they are very heavily bent in reducing and reusing, so I try, as best I can, to align myself with their goals. The bike shop is a small part of the centre - they grow flax to make clothes, have a solar kiln, grow vegetables to supply to low income homes, a stained glass workshop, a wood working shop, a smith forge, they are a place of refuge for emergencies, etc. The lady who runs the place lives in a sod house, that is how dedicated she is.
She’s a great lady and pretty much gives me free run to decide on how to address each bike.

Anyway, I just want to see how well I could refurbish it..I’m retired now….keeps me out of trouble,

i've never had luck trying to get those out without the wrench... to twist the top tab in an attempt to remove the cap will end up breaking the adjuster, and the cap will remain in the tube, making a bad fork useless.


after cleaning.and regreasing multiple examples of that fork, i recommend replacing them with a better fork before charging someone to refurbish a barely-worth-having boat anchor...
your situation precludes that path of action.

i use 400 grit emery paper for HEAVY rust spots, then 1000 grit for second finish, then fine steel wool or 1200/1600 as a final finish... work in line with the tubes, not around them.
avoid using tan Carpenter's Sandpaper.. it is of poor surface control and makes hit/miss deep scratches

the most annoying failure of those forks is when they fill with rainwater, and then the guide bushings get hydraulicked out of the lower tubes when someone forces them to move again...

proper grease is RockShox Judy Butter or equivalent... thick axle grease will not work well... a light axle grease is kinda ok, but still too sticky, IMO.
it only takes a light coating on the lowers and springs, a tiny smear on the upper tubes...... if you use too much, those annoying bushings might become adrift.

This tool worked quite well. It is what I use to change the saw blades on my table saw.

I’ve stripped and repainted 3 bikes in the past and oil coated steel wool does work great to remove rust then I used 800 grit finishing sandpaper and, no, not the carpenters sandpaper.

Agreed, these forks are more gimmicky than they are suspension. It has, not only, a steel 1 1/8” steerer tube (thank you for advising me there) but it also has steel sliders. They did clean up pretty good but still a tad pitted.

Anyway, I was able to clean them up with some suspension specific grease inside and they bounce/slide smoothly and, seemingly, unaffected by the small amount of pitting on the sliders.

It is a bike that will either be given away or sold for about $50, depends on level of income of the person buying.