Q:

Can i use larger/smaller circular saw blades on my circular / plunge / table / miter saw?

I own a plunge saw and a miter saw. Can I use blades from one saw on the other saw?

A:

Especially within the same size class of saws (eg. 8.5", 10", 12") you will find that machines sometimes have blades which differ in size up to 5 mm / 1/5" (12": 300–305 mm, 10": 250–254 mm). For the less common sizes the size difference might be even more obscure: consider Mafell’s MT55 requirement for 162 mm blades, which is slightly smaller than 6-1/2" (165 mm).
Disclaimer: To avoid injury you should always only use circular saw blades recommended by the the manufacturer for the model of circular saw you are using. The following answers are from my personal experience with working with many different saws on a daily basis. Follow the advice on your own risk and use common sense when doing so.

Can I use larger blades?
Short answer: No.
Long answer: You should only ever use larger circular saw blades, when the difference is fairly negligible (1 mm / 1/16").
The reason for that is that for safety reasons most saws are built to tight tolerances. The tolerances accommodate slight differences in size due to production tolerances or design differences for the same diameter saw blade. Especially with newer models these tolerances are fairly small. Using a larger blade risks damage to the tool and danger of injury from resulting debris.
Blade geometry: Make sure the blade you want to use is built with a geometry intended for the type and model of saw you want to use it on. The angle of the teeth is usually significantly different on miter saws where you can clamp down the material to be cut. Also make sure that the kerf,  blade width and max RPM speeds are compatible.
Asserted force: The more powerful your circular saw is and the larger your blade diameter becomes, the more your circular saw’s motor has to work to apply the same torque to to the teeth of your circular saw blade. This can lead to increased stress on the motor and the motor burning out prematurely.
Example: A 216 mm / 8-1/2" circular saw blade will not fit on a Festool TS-75 (210302.4 mm, or 8-1/4"). Even though you adjust the riving knife, the larger diameter of the blade will not clear the blade housing.

Can I use smaller blades?
Short answer: Within reason, you can.
Long answer: For safety reasons the blade gap should not be larger than 1/8" (3 mm). If you do not care about workplace safety, you can use smaller circular saw blades in most cases.
Blade geometry: Make sure the blade you want to use is built with a geometry intended for the type and model of saw you want to use it on. The angle of the teeth is usually significantly different on miter saws where you can clamp down the material to be cut. Also make sure that the kerf,  blade width and max RPM speeds are compatible.
Asserted force: The more powerful your circular saw is and the smaller your blade diameter becomes, the more force (torque) is applied to the teeth of your circular saw blade. Depending on blade geometry (teeth geometry, material, kerf) this can be an issue when the used blade is significantly smaller.
Cutting depth: Depending on the type of saw you need to adjust for the reduced cutting depth.
Miter saws: The nature of the technical construction of miter saws limits the reduction in size. Any further reduction will prevent you from making cuts. On miter saws the reduced diameter will also result in accelerated blade wear (as you cannot adjust for the reduced cutting depth).
Dado blades for table saws: The only case where it might make sense to use a significantly smaller blade on purpose, is when you install a dado blade set on a low powered table saw. See Can I use an 8" dado blade set in a 10" table saw?
Example: It is safe to use a 160 mm blade on a Mafell MT55. In fact Mafell offers both 162 mm and 160 mm blades for the MT55.

Can I use blades with a different kerf / blade width?
Short answer: No.
Long answer: Within reason you can.
Kerf: From my experience if the difference in kerf is reasonably small (max. 0.2 mm, or 1/120") it should work out just fine.
Different blade width: Depending on the mechanism for mounting the blade to the hub you can use different blade widths. Refer to your owner’s manual to determine which blade width is okay to use. Using out of spec blade width can lead to wobble, increased wear, and damage to the motor, hub and blade housing.
Example: I am using a circular saw blade with 2.8 mm kerf / 1.8 blade width on a Festool TS-75 without issues. The owner’s manual states a blade width of up to 1.8 mm and a kerf of 2.4–2.6 mm. Festool officially sells blades with a kerf of 2.2–2.6 mm for the TS-75.

