There are four primary types of threaded junctions that you will find on your Bearhawk. The first and the most common is the “fine thread” UNF (Unified National Fine) threads that you’ll find on AN bolts and nuts. Examples of fine thread are 10-32, and 1/4-28. The first number is the diameter, and the second is threads per inch. You can find aircraft-grade hardware with UNF threads at places like Wicks, and Aircraft Spruce. You can find taps/dies with these threads at better-stocked hardware stores. We always recommend using aircraft-grade hardware from aircraft-grade sources whenever an aircraft-grade product is available. In addition to having a more likely pure pedigree and assured minimum strength, aircraft grade bolts have a longer shank section relative to the length of the threaded section. Consult the Bingelis books and AC43.13 for much more detail. You’ll be assembling and disassembling many parts, so it may be a good idea to use plain nuts until approaching final assembly. Nylon lock nuts lose effectiveness with after the first use.
A close relative to UNF is “coarse thread” or UNC (Unified National Coarse). These are the most common threaded bolts in almost any hardware store, and you’ll find them in many places on Lycoming engines. Bob often specifies UNC when female threads are cut into aluminum, as in the bolts that secure his gascolator design. When using these bolts, it can be difficult to find aircraft-grade parts. Look for grade 5 bolts, which will be marked with three radial lines, like this:

Often the bolts in the big-box home improvement stores are lower grade with no marks. Avoid these. Also, be careful about using grade 8 bolts, which will be marked with 6 radial lines instead of three. One might think that stronger is better, but these bolts can be more brittle. Examples of coarse threads are 10-24, and 1/4-20.
Another common thread type is NPT, or National Pipe Thread. These threads are what you’ll find in much of your plumbing, and in several plugs in the engine. NPT threads are tapered, and threads on fluid-carrying NPT fittings require additional sealing to prevent leakage through a helical-shaped gap between the ridge of the male thread and the valley of the female thread. Don’t use teflon tape on aircraft threads, because the risk of getting bits of it in the system are too great. One suitable product is Loctite 565.

The final threaded fitting you’ll encounter is the flared fitting, as is used at the end of most flexible fluid lines and hard fluid lines. These fittings require a 37-degree flare, which is specific to aviation. The seal is made when the faces of the flare make contact, so there is no need to seal the threads. Don’t use automotive tools unless you can be sure that they are made for a the 37-degree flare. They are probably not, unless they are sold to the race car industry.