The size of the bolts that attach your toilet seat to the toilet bowl can vary depending on the model and manufacturer of your toilet. However, most modern toilets use either 1/4-20 UNC bolts or M6 bolts.
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Common Toilet Seat Bolt Sizes
Here are the most common toilet seat bolt sizes you’re likely to encounter:
1/4-20 UNC
This 1/4 inch, 20 threads per inch bolt is the most common size used on modern toilets in the United States and Canada. The “UNC” stands for Unified National Coarse thread.
M6
The M6 size bolts with 1 millimeter thread pitch are commonly used on toilets in Europe and other parts of the world. M6 bolts have a diameter of 6 millimeters.
Others
While less common, some older toilets may use:
- 5/16-18 UNC
- 3/8-16 UNC
- 10mm
Identifying Toilet Seat Bolt Size
If you’re not sure what size bolts you need to buy, there are a couple ways to identify the bolts on your existing toilet seat:
Measure with Calipers
Use a caliper or measuring tool to measure the diameter of the bolt shaft and count the number of threads per inch.
Bring Sample to Hardware Store
Remove one of the bolts and bring it with you to the hardware store. They can help you identify the thread size and match it with new bolts.
Consult Toilet Specs
Look up the specifications for your toilet model online or in your manuals. Some brands like American Standard may list the toilet seat bolt size in the technical specs or repair parts list.
Choosing New Toilet Seat Bolts
When choosing replacement toilet seat bolts, make sure to get bolts specifically designed for toilet seats. Look for:
- Stainless steel bolts – resist rust and corrosion.
- Washers and caps – provide extra security.
- Bolt length – should fit toilet bowl thickness.
Avoid using standard machine bolts, since they are not designed to handle the moisture environment inside the toilet tank.
How to Replace Toilet Seat Bolts
Follow these basic steps to remove your old bolts and install new toilet seat bolts:
- Turn off water supply valve and flush to empty tank.
- Remove old seat and bolts using pliers or wrench.
- Clean bowl surface thoroughly where new seat will attach.
- Insert new bolts through seat holes and toilet holes.
- Install washers and caps; tighten bolts.
- Reconnect water supply and test for leaks.
Be careful not to over-tighten the bolts when installing the new seat. Tighten just enough so that the seat feels stable and doesn’t rock. Overtightening can crack the porcelain.
Conclusion
While toilet seats may seem mundane, using the right sized bolts to match your toilet bowl is important for a secure, leak-free connection. The most common bolt sizes are 1/4-20 UNC and M6, but you can always measure your existing bolts or bring them to the hardware store to find the right match. With the right bolts and proper installation, your new toilet seat should provide years of dependable service.