I have a Ryobi router that loves to completely lock up like I suspect yours did. I keep a tool very similar to the one pictured below handy to motivate it back open when necessary.
For $14, it's probably something worth having around, and it's a cheap test for whether the router is just stuck.
Ok, revised my answer
I found the instructions here and the information is on page two under "Set-up: Fixed and D-Handle Base - ADJUSTING THE DEPTH OF CUT (FIG. 1, 3)"
Occurring to this there is no lock of the black adjustment ring so it should turn somewhat freely, though it might have some resistance so not to move when you don't want it it.
It's very ...
You have a 'Stanley knife'? - common UK name for a generic tool I know of no other name for.
Hold wire against knife with thumb.
Carefully push thumb so wire rotates.
Stop before blade reaches thumb.
Pull end of plastic insulation off.
if it fights you a bit, drag the tip round in a circle, putting pressure on each side in turn.
This has been the trade ...
Greenlee 1161 Adjustable Fiber Jacket Stripper
I used to use these until I learned how to just do it with a utility knife.
If the jacket is loose enough, you can try these.
"Slitting blade [not visible in picture; it's inside] rips outer jacket of NM cable cleanly and quickly"
IDEAL Lil' Ripper Wire Strippers
I've owned "The best wire ...
Being stingy, and not averse to minor personal injury I'd attack the white outer with my trusty pocket knife,
The idea is to cut it most of the way through the white layer and then flex the cable until it tears the rest of the way though.
Cutting while flexing works well too.
For speakers, losing a couple of strands of the wire itself is irrelevant. I know that some of the wire mfrs hawk their "gold plated" wire and make a huge deal about conductivity, but in reality it's all bunk. 16ga wire is rated for 10A, even a typical 350W speaker is going to draw maybe 6 to 7A.
With experience, you can just cut the outer insulation (trick being, not all the way though - you make a weak spot/stress concentration by grooving it, and then pull off the waste, and it breaks where it's been grooved.) You can practice by cutting off less of the outer sheath than you need a few times, so any nicks on the inner insulation would be stripped ...
If you cut away enough plastic to grip the metal, you may weaken the joint. I would drill a hole on the opposite side of the exposed pin large enough to start a metal punch in. Some places it is called a drift or pin punch as found in a Google search. Once the hole is drilled, set the exposed pin over a hole it can drop into that is sturdy, like a drilled ...
This looks like a hinge of some sort. If the space between the upper and lower plastic parts is accessible, or if it's hidden behind a shroud and you're willing to cut the shroud away, then try inserting wedges between the plastic pieces to force them apart. In other words, rather than pulling the bar out of the plastic, pull the plastic off the bar. The bar ...
If you can cut it with an xacto you can cut it with a razor blade utility knife (aka carpet knife, Stanley knife), like this:
The blade is thicker and more durable than an xacto, and the handle allows you to apply more power to the blade.
My option 1 would actually be a rotary cutting tool like a Dremel with a cutting wheel attached, however it's an ...
If there's a window, you don't need a dipstick.
If there's no lower outlet, open the inlet and turn it over. Or, suck it out (auto parts stores typically have something for doing that.)
Compressor oil changing does not need to be especially convenient as it's relatively infrequent, and the scale of compressor you show is not impossible to turn over by hand ...