I wonder if we're talking about
real Sperzels here. There are some look-alikes out there such as these parts from
Guitar Fetish...
They're supposedly Gotoh parts, but they
look like Sperzels and purportedly do the same job. They're very attractive because they're $30 vs. the $75+ most places want for genuine Sperzels, even though they look exactly the same. It's hard to ignore a savings like that, no matter how nationalistic you are.
But, there are differences. One of them is that these don't use a loose locking pin like the Sperzels do. They advertise this as a desirable feature, citing the inability to lose the pin (does this happen to anybody in real life? It's ok - you can admit that you're stupid enough to unscrew your lockers so far the back falls off - we'll still love you). But, it means they're turning out the locking knob/pin as a single part, which says they're being turned out on a screw machine. If that's the case (and I'm fairly sure it is) then the parts haven't been hardened. If they aren't hardened, then the thing is only going to work a few times before the face of the locking pin is all deformed and the likelihood of it developing any real tension and grip on the string goes way down.
Then, pliers? Gimme a break! Even if they are real Sperzels, that's like trading a mousetrap for a land mine. Dead is dead - you can stop once you reach that point. Any more force is wasted. All it takes is manual finger torque to get those things tight enough to do their job. That's what they're designed for. Anything more than that and you're
way outside the envelope and all bets are off. The thing is probably ruined the first time you reef on it like that.
Edit: I don't mean to disparage the Gotoh parts - I had a set of those some time back on another guitar and they worked just fine. The reason I don't use them any more is I'm not confident that the locking post to tightening knob joint can withstand repeated use even if it's machined from a single blank. It's a mechanically inferior design, albeit much less costly to manufacture. I have to admit I never experienced a failure, but I also didn't subject the things to extended use. That guitar is long gone.