This is a fire hydrant birdhouse with 1-5/8" diameter entrance. I added several drain holes on the floor and added holes in center of the three nuts to act as ventilation. A hole was also added at the bottom of entrance hole to minimize water funneling into the birdhouse.
I added chain links to the nuts around the fire hydrant for some realism as well as using real bolts to bolt the top to the body (I used M6 socket cap head screws instead of hex head bolts which would be better. Its what I had laying around the house). M6 or 1/4" bolts will work.
Super glue was used for the birdhouse, I also super glued middle of the chain to the body of the birdhouse. I noticed the chain hitting the birdhouse made quite a noise, I'm assuming birds wouldn't like it so much.
3 of Side Cups
3 of Nuts
1 of everything else
~ 1 to 1.5 ft of small chain (3/8" length linked)
Qty 6 of (M6) or (1/4-20) Hex head bolts 16mm or 5/8" L