Forgot to give dimensions and now I own a bottle opener the size of a quarter

Been on the other side of this one. I run the Tormach in our small shop and a coworker asked me to make him a bracket for his phone mount in his truck. No dimensions, just 'you know, phone sized.' I measured my phone. His was a whole inch bigger and he mounted it before checking, so the thing cracked at the corner the first time he hit a pothole. We both learned something that day, mostly him.

What I started doing after that is keeping a stack of index cards by my desk. Anyone who wants a favor part fills out one with the three numbers that acutally matter, length, width, thickness, and where the holes go if there are holes. Takes them thirty seconds and saves me a remake. One thing I'd add to the sketch plan: include the material thickness too, not just the outline. I've had people hand me a drawing with a nice profile on it and zero mention of how thick the stock should be, then act surprised when I picked 1/4 inch plate and they wanted something that fit in a pocket. Glad he offered to rerun it though. Around here a second part out of scrap costs nothing but his time, and he clearly enjoys making them, so you might end up with two openers anyway. The little one can live on your keys.

I'm the opposite problem at my place, I hand people dimensioned sketches for everything now, even dumb stuff, because of a card holder I had cut from a piece of 1/4 inch 6061 years back. I sketched it on a napkin with one arrow and the word 'pocket.' Came back with a pocket exactly as deep as I drew, which was three times what I needed, so the cards sat an inch down where I couldn't grab them. My fault entirely, the guy followed the napkin to the letter. What fixed it for me was a habit: I write the number next to every arrow, then hand it over and say the units out loud. Half the arguments in our little garage shop have been inches versus millimeters, not missing dimensions. The sketch with all the numbers still looks like chicken scratch, but at least it's chicken scratch that fits.

Disagree a bit with the index card thing. Three numbers and hole spots still leaves way too much to guess. I handed a guy exactly that for a shelf pin jig block once and got back something an inch too long because neither of us thought about where it stopped against the cabinet side. The card needs a sentence about what the part does, not just the dims. If I had written 'stops flush against the back wall' on it, he'd have known the length was fixed, not flexible. Dimensions without intent are just half a sketch.

Update: brought a real dimensioned sketch the next morning and the new one came out exactly bar-sized, works great. But now I'm hitting what the shelf pin jig guy was saying, my sketch had three numbers and he still had to ask me about edge break and wheather to chamfer the opener slot. How much detail do you all actually put on a sketch for a favor part?