This is my first model I made myself. It is simple, but I got to play around with adding fillets, sketches, etc. to learn. 

This 810 drip tip is being used on my Dead Rabbit Squonk RDA and fits nice and snug, no wobble! I made it slightly larger diameter to account for some shrinkage. 12.75mm for the insert and shrinks down to 12.50mm perfectly. 

I printed mine upright with supports, and tried it upside down without. Both came out the same, though the supports leave some material on the lip if you aren't careful, so I advise printing it as I have it in the print profile. 

My RDA has a single o-ring inside and the dimensions are as follows

17mm outter diameter, 5mm insert, 12.75mm diameter to outer wall of insert (shrinks to 12.5mm), and 7mm top portion (where the lips go).

Fillet on the mouth piece, both inside and out, 2mm. 

I advise printing this in PETG if you are close to the coil, but I made mine in PLA+ to test and because I want to make a silicone mold and cast is in resin or something else. Should hopefully fit other 810's but I could only test it on the RDA that I have. 

Let me know if it fits and works for you!