Wood fixed-pitch propellers should have their bolts loosened and the propeller removed, inspected, mounted, retorqued, and safetied quarterly, at a minimum. By “safetied,” the bolts or nuts can be safety wired or secured with cotter pins, depending on how the propeller is secured. More frequent retorquing may be required depending on the climate where the propeller resides and flies.
While you have the propeller off, it would be a good time to inspect the propeller, spinner, backing plates, nut plates, etc., and correct any issues you may find.
Engine torque is transmitted by static friction between the engine’s drive flange and the rear face of a wood prop. At the fundamental level, coefficient of static friction multiplied by clamp force determines torque capacity.
Be sure to carefully clean the engine flange and prop face. Some installations sandwich a spinner backplate between the flange and prop. The backplate must also be clean, as anything in the sandwich which would lower the available static friction can lead to slippage and failure. Note “anything” can include spinner backplate material, varnish, and coatings. Exposed carbon fiber, for example, has a very low coefficient of friction, but if the carbon is fully encapsulated in epoxy, the available friction remains relatively high.
Bolt toque is a proxy for clamp force. Available clamp force is limited by the wood’s crush strength perpendicular to the grain, which varies widely with species. Bill’s illustration shows 42 ft-lbs for a Catto, which suggests 1/2″ bolts and a maple core. Although correct for the Catto, it would crush a softer wood. For example, the correct clamp force for a classic yellow birch Sensenich on an A-65 Cub is created with six 3/8″ bolts at 15 to 19 ft-lbs. A custom prop in a soft mahogany might be limited to as little as 12 ft-lbs. The prop manufacturer will specify correct torque. Don’t be tempted to increase the specified value. More is not better.
I have a wood propeller. Mark Zeitlin recommended belleville washers under the bolts. These work and hold the torque and you can re-torque at annual. The first year i check torque at ten hour intervals, but the torque was ok. The second year I checked at annual and torque was fine.