Drawing shiny hardware - how do you get the metal look without it going flat?

I lean toward pushing the contrast harder than real life, honestly. I did a series of old wrenches in graphite last winter and the ones where I kept the values tame just sat flat on the page. What worked for me was picking one or two spots where the light really bites, usally the edge where the serrations catch it, and letting those go near white while keeping the rest of the midtones honest. The eye forgives exaggeration in one or two places but not everywhere at once.

I also go the opposite direction with my build-up than you did. I lay down a light overall tone with a graphite powder wash first, almost like priming the paper, then work darker into the shadows and lift back out for the sheen. On smooth Bristol it lifts clean enugh that I can pull highlights with a regular eraser pencil. Tried it on a toothier sheet once and the highlights came out muddy, so paper choice matters as much as technique. One thing that helped with the metal-versus-plastic problem was studying how the reflections acutally run on hardware sitting on my bench. Polished steel has hard, defined breaks between light and dark, plastic blurs them. If your transition zones are crisp even when the values are softened, it still reads as metal.

Would love to see what the thread pitch ends up looking like if you draw a bolt to go with those nuts.

I've had the opposite expirience with metal, funnily enough. I drew a set of old gate hinges and a couple of bolts for a still life last spring, and every time I cranked the highlights up the whole thing started looking like chrome on a car, not steel that's been sitting on a fence for twenty years. What finally made it read as metal was keeping the values in a narrow band and putting all my effort into the texture, the little nicks and the grain of the casting. The eye does a lot of the work if the surface pattern is believable.

On the flange serrations specifically, I'd try treating them as a repeating rhythm rather than a light source. If each little tooth gets its own tiny dark and light pair, consistent across the ring, the metal reads as machined even when the overall contrast stays quiet. That was the trick that saved my hinge drawing, anyway. As for order of working, I go the other way from you. I lay in a light middle value first with broad strokes, then push the darks in gradually, saving the eraser for the very end as a finishing tool rather than the main event. When I start dark I always seem to run out of room to go darker, and then the highlights have nowhere to live. Worth trying on one nut and comparing it side by side with your usual method before you commit either way.

One trick that helped me calibrate the values was taking a phone photo of the drawing in black and white next to the actual nut under the same lamp, becasue the camera flattens everything and shows you instantly whether your midtones have drifted toward mush. I did that obsessively with a drawing of a socket wrench and it saved me from at least three rounds of pointless reworking.

Also, with charcoal on anything this small, I find the serrated flange edges want a sharpened pencil stump or even a hard charcoal pencil rather than the soft stick, otherwise the teeth blur together and you lose the ratchet-like rhythm of the pattern. Were you using vine or compressed for the shadows? Compressed holds an edge much better on detail that fine.

On the dark-to-light question, I'm with your instinct. I did a big cast iron pulley wheel in charcoal last year and blocking the darks first saved me, because charcoal goes down heavy and there's no erasing your way back to a clean dark once you've got graphite dust all over the page. The downside is the highlights get fragile. I had to keep a sharp craft knife next to me to trim my kneaded eraser into a point for the tiny glints on the bolt faces. One thing I'd try with yours is photographing it upside down, my brain stops seeing a nut and suddenly the wonky values jump out.

The serrations are what'd scare me off, honestly. I tried drawing a wing nut a while back and that little knurled edge just turned to mush no matter what I did. Ended up having way better luck drawing them bigger than life, like 3x size, so each tooth actually had room to exist. Shrink it down to real scale and there's not enough paper to work with.

Also, do you work from an actual nut sitting on your desk or from photos? I found the real thing beats photos for metal because you can tilt it and watch how the sheen moves, which teaches you what you're actually drawing.

Update: tried the phone photo trick from earlier in the thread, taking a black and white shot of the drawing next to the real nut under the lamp. Turns out my midtones had drifted way mushier than I thought. Fixed that, then pushed contrast on just one edge like the wrench person suggested. Now I'm wondering, does that selective approach work on the serrated flange too, or does it read wierd on textured surfaces?