Attached Limb Systems (Garnier Limbs)
 Garnier
Limbs (aka GLs) are the best known of all the "attached limb system" designs and the term "GL" has become
synonymous with a heavy bolt of any kind that serves to perch a load in a tree. A Garnier Limb is the universal idea of
installing a "branch" where one is needed. Collectively all limb system designs have been
referred to as "Tree Anchor Bolts" or TABs (machine shop talk). The GL is what started it all nearly 10 years ago.
GLs are a high strength solution for supporting treehouses. Endorsed and extensively experimented with by Michael Garnier, of the Out 'n' About Treesort in Takilma, Oregon. Michael directly influenced (and inspired) arborists, engineers and builders to chime in and contribute completely to the improvement and betterment of this arborially sensible system. Subsequently, these highly modified bolts evolved and filled a clear need to have a device that was capable of withstanding significant shear forces, better than any hardware that came "off the shelf".
The basic GL is made from machine threaded 1-1/4" (4140) steel round stock with a unique flange (aka cuff, collar, boss). In the photo above, the threaded area to the left of the flange penetrates the tree into a specifically shaped hole. The hole is drilled using a specialized bit which allows the flange to fit flush with the heartwood when fitted. The longer collar systems (more typically used these days) are designed to allow the tree to grow over and around that portion of the extra long collar that is left exposed on the outside of the tree. This allows better sealing and encourages the compartmentalization process that the tree biologically goes through as it recovers from the original penetration.
The resulting anchor point can routinely withstand loads of up to 8000 lbs.—up to 30,000lbs. in the case of some Heavy Limbs (HLs)—next to the flange, making it ideal to support heavy beams and long knee braces. Extensions can be fabricated to allow the 'artificial limb' to be as long as is necessary. The far end of these cantilevered extensions can then be suspended or braced.
Numerous applications and variations of the basic GL system as a support and component of larger brackets that accept fitted wooden support beams have been developed and used by THW in their custom built treehouses.
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