Treehouse attachment bolt

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

Treehouse attachment bolts (TABs) are special bolts used to attach a treehouse to a live tree with minimal damage. There are several styles and brands, including Garnier limbs (GLs), artificial limbs, heavy limbs (HLs), tree anchor bolts, and stud tree fasteners. Some are through bolts for smaller trees, while others are side-mount bolts for larger trees.

Key features
- Very strong: TABs can carry about 9,000–12,000 pounds, far more than typical lag bolts.
- Fewer tree penetrations: They grip more of the tree with less cutting, helping protect the tree.
- Design: A typical TAB has a threaded bolt, a large collar, and a long perch ending in a nut. The collar spreads the load across the tree grain to reduce bending damage, and the long perch keeps the lumber away from the trunk to allow for the tree’s growth.
- Movement with the tree: TABs are usually used with pipe brackets so the structure can shift with the tree and avoid rigid restraint.
- Material: They’re made from spring steel to handle the up-and-down loads caused by wind.

Origin and design notes
- The idea of using a collar or large piece to increase strength in wood goes back centuries, to concepts like shear plates that improve load capacity.
- Michael Garnier started building treehouses in 1990 in Oregon. After early regulatory challenges, he developed the Garnier limb, a strong alloy-steel bolt that can be screwed into the tree trunk.
- In the late 1990s, Garnier collaborated with others and released commercial versions called Artificial Limbs. An improved collar (a 3-inch collar on a 1.25-inch hex bolt) was added to maximize surface area and reduce pressure on the tree.
- Garnier became the main producer of these bolts, known as Artificial Limbs and Garnier Limb.