The Adams, without a doubt, is one of the most popular dry flies ever invented and I believe a size 16 might be the best selling size. So, here's an Adams Dry tied on a size 16 standard dry fly hook.
Start your thread behind the hook eye taking several wraps to secure it to the hook shank. Leave the thread at the tie-in location for the wing. This should be at a point 2/3rds to 3/4's the length of the hook shank.
Select two neighboring hackles that look to be the appropriate width and outline for your wings. Orient the hackles so their shiny sides are facing each other and so their tips splay out. Grab the tips and pull the lower fibers back to expose a wing segment about the length of the hook shank. Check it's length against the hook shank before tying it in. Anchor the wings to the hook at the tie-in point with 3 or 4 nice tight wraps before snipping off the butt ends. Pull the wings up and back, and build a thread dam in front of them to prop them up. Separate the wings with a few cross wraps between them followed by a figure 8. Now take a couple of wraps to lock everything in place and prop the wings up.
Select a hackle from the outside upper edge of a grizzly cape. These hackles generally have nice, stiff, straight barbs, perfect for tailing material. Select a brown hackle from a similar location and with like-sized barbs, and then align the tips and stems of the two feathers. Pull a segment of mixed brown and grizzly barbs from the hackles, this will be the tail of your fly. Save the two feathers as you can use them to make tails for multiple flies. Snip the little curlies off the tail fibers and measure them against the hook shank. The tail should be somewhere between the length of the hook shank and the full length of the hook. Take a couple of loose wraps to secure the bundle to the top of the hook shank. You can make minor adjustments to length if necessary. Wind the thread all the way back to just before the bend of the hook. Then wind your thread forward just a bit.
An Adams Dry is traditionally dubbed with muskrat fur but here I'm using Adam's Grey Fine and Dry Dubbing. Thin layers of dubbing are always better than thick. Remember, it's much easier to put dubbing on than it is to take it off. Now wind back so the dubbing starts right at the tail then wind forward to form a nice tapered body. There's no rule that says you can't wrap backwards to fill in a gap or a low spot, the body should end with a small space behind the wing.
A quality hackle gauge takes the guesswork out of selecting the appropriately sized hackle for your fly. To really get an accurate reading, take one or two full wraps around the pin of the gauge. You can see here the very tips of the barbs land within the size 16 range. To prepare the hackles for tie-in, face the dull underside of the feather toward you and then pull the very bottom fibers down and snip off both sides. Now, and this is important, strip about 1/8 of an inch of fibers from the top side of the feather. This will help to insure that the hackle is wound correctly. With that space facing up, tie the hackle in behind the wing. Now repeat this same process with your other hackle and tie it in. Wind your thread forward to about 1/16th of an inch behind the eye. Wind the hackle you tied in last around the hook shank, away from you. Notice how that barb-free space on the hackle helps the feather to orient correctly. Take 2 or 3 wraps behind the wing then pull the wing back and take a wrap immediately in front of it. Take 1 or 2 more wraps but leave a little space behind the eye. Now take a single wrap with your tying thread around the hackle. Pull the hackle back and take several wraps to pin the hackle stem back. You can then carefully snip the hackle stem off close.
Now wind your second hackle in the same manner, zig-zagging your way through the previous hackle. Again, take one wrap around the stem to secure it to the shank. I like to use a half-hitch tool to press the barbs back before taking the wraps to pin the second hackle. This helps to prevent trapping barbs against the hook eye. Now, snip the hackle off short. If you did collect some barbs, now's a good time to trim them off.
Carefully whip finish the fly, trying your best not to trap barbs. You can then snip or cut your tying thread free from the fly. Apply head cement if you like and you're done.
If I was allowed to fish with only one dry fly, I'm pretty sure it would be a size 16 Adams.