By definition lag bolts are actually lag screws, but as you've probably noticed they are more commonly referred to as lag bolts. The most popular & most common type of lag bolt is the hex style or hexagonal (six sided head) and these are used to secure wood to other wooden, concrete or masonry types of material. One example is in the construction of a tree house for the kids, where you'd be better using tree house lag bolts, as the name suggests. These are looked at here
One advantage of these types of fasteners is that they can be used without needing a pre-drilled hole or with a smaller sized pre-drilled hole to prevent wood from splitting. As you're aware, a kids tree house isn't the same as building an extension to the home or workplace, so it's very important to ensure they are used correctly and offer the safety that would be expected. Lag bolts should be used with an appropriate lag expansion anchor for concrete and also masonry construction applications.
Threads for these lagbolts will vary according to the individual required bolt sizes and dimensions. That being the case though, ISO standards for threads are set out as this: The bolt length is twice the diameter of the bolt plus ½ inch, so this makes ordering / purchasing much easier. Various sizes of lag bolts can be purchased here.
Why Stainless Steel Lag Bolts ?
Hex Head Lag Screws are available in various finishes. These include Zinc Plating for moderate corrosion resistance. For higher corrosion resistance you should be looking at Hot Dipped Galvanized bolts. An even better option is 18-8 Stainless steel which offers you the highest level of corrosion resistance.
Both Hot Dipped Galvanized and 18-8 Stainless Steel are as a rule of thumb generally intended for use in outdoor & also marine applications, as well as with any type of treated lumber. So if you're wanting outdoor use and the weather generally isn't great, then stainless steel lag bolts are the way to go.
You can order your Hillman 832012 1/4 x 3-Inch Stainless Steel Hex Lag Screws HERE