I lived with a wobbly toilet seat for eight months. Every time I sat down it shifted half an inch to the left. I told myself it was a complicated plumbing job. When I finally looked at the underside of the toilet, I realized it was two plastic bolts. I had been annoyed for eight months over something that took four minutes to fix.

The two kinds of bolts you will find

Flip up the plastic covers at the back of the seat — the little round caps where the seat meets the bowl. Underneath are either:

• Plastic wing nuts. Turn them counterclockwise by hand. If they are stuck, grab them with pliers, but go gently — the bolts are plastic too and they snap.
• Metal bolts and nuts. Older toilets. Use an adjustable wrench or a deep socket. Spray with penetrating oil and wait ten minutes if they are rusty.

Once the nuts are off, lift the seat straight up. The bolts should slide out through the holes in the porcelain.

Buying the right replacement

Toilet seats are not universal. You need two measurements:

1. Bolt spread. The distance between the two mounting holes, center to center. Standard is five and a half inches. Measure it anyway.
2. Bowl shape. Round or elongated. Round bowls are about sixteen inches from bolts to front edge. Elongated are about eighteen. Hold a tape measure — if the number is closer to sixteen, buy round. Closer to eighteen, buy elongated.

A mismatched seat overhangs or leaves a gap. Both look bad. Both feel worse.

Installing the new one

1. Line up the bolts through the mounting holes. Most new seats come with the bolts pre-installed in the hinge mounts.
2. Thread the nuts from underneath. Tighten them by hand first, then give them a quarter turn with pliers. Do not overtighten — the bolts are plastic and the porcelain will crack before the bolt gives way.
3. Adjust the seat position. Most seats let you slide the hinges slightly before final tightening. Center the seat so it does not hang off one side.
4. Snap the covers down. Those little plastic caps press into place. If they will not snap, loosen the bolt a tiny bit — the nut might be pinching the cover mechanism.

When the old bolt snaps

It happens. The plastic gets brittle. If a bolt breaks off in the hole, do not panic. Grab the broken stub with needle-nose pliers from underneath while turning the head with a flathead screwdriver from above. If the stub is flush with the porcelain, use a hacksaw blade to cut a slot in the top of the bolt, then unscrew it with a flathead.

Four minutes. Two bolts. Eight months of annoyance that I could have avoided by just looking.