My IA once remarked gently, after handing a tool to me, that there are two types of people - those whom, when handed an unfamiliar tool, look at it briefly and hand it back, and those that examine it, note the manufacturing marks, the wear marks, and the modifications, and try to figure out potential uses.
He said this not long after handing a modified once-a-wrench to me. I'd puzzled over it briefly, then handed it back while asking what it did.
Tonight, keeping a friend company while he cleaned up his workbench and organized his toolbox (I'M not fool enough to try to organize another man's toolbox!), he kept handing things to me as he found long-lost items. Mind you, he works on cars, and on model airplanes - and between the two, my own tool sets have more in common with his model airplane tools. (I don't own any sockets bigger than 1/2 inch - why would I need to, except for my oil filter?) Still, he handed a round chunk of black steel to me. I frowned, turning the cylinder over in my hands. "Hmm. A breaker bar clearly goes in here. So that means this must be a very deep socket. A very deep, very huge socket. With four little contact points... I have absolutely no idea. What on earth is this huge?"
"That is a socket for Dana hub for four wheel drive." He grinned, and handed a part of... something to me.
"There's a gasket that goes here, and that..." I shoved the tip, gently. "Yep, that's a needle valve."
I stared at the capped end, thinking that it looked like a diaphragm, but... not right. Flipping it over in the dim light, I squinted into the two holes on the underside. "Something goes in and out here. And..." I puzzle over it, squinting, getting no information from the stamped part number.
"Here's a hint. It's from a 1986 Ford, which was the first year the engine..."
"Fuel injection!" I exclaimed, nodding, and regarded it again. "This is part of the fuel injection! Which part, though?" I continued to turn it over, trying to figure it out.
"You got it. This is an idle air control valve for a 1986 Ford Bronco, that bypasses the butterfly valve..."
Yeah, I'm not there yet, but somewhere, my IA is chuckling behind his coffee mug just hard enough that the exquisitely waxed points of his mustache are quivering. He knew, all those years ago... and I am still a young grasshopper yet, but I'm learning.