What are the differences between Treehouse Attachment Bolts and Garnier Limbs?
Similar in Theory, Slight Variations in Specs.
Specs for TABs vs. GLsBoth Treehouse Attachment Bolts (TABs) and Garnier Limbs (GLs) are made from 1.25" 4140 steel rod. The wood threading is then turned onto the inner end, a 3" diameter collar is either shrink or interference fit onto the center, and a nut is threaded onto the outer side. Various versions have differences in the length of material that fits inside the tree, so drill bits are not always compatible between manufacturers. Predrilling a 3" hole in the tree is required, so special order drill bits are typically required for installation. We use a national fine thread on the nut end of the TAB, while some other versions use course threading. All Treehouse Attachment Bolts on this website are heat treated. Some
other manufacturers of TABs do not always do this, so make sure your
engineer will accept non-heat treated bolts - they are okay in some applications. The powder coating finish
is our preferred method to inhibit rust without using toxic chemicals.
Using nothing (bare metal) or a simple spray paint will offer only
minimal rust protection, but it does save a few bucks. In some cases, we can't be exactly sure of the specific differences if our competitors do not disclose their exact specs.
These treehouse fasteners are a derivative of the 150 year old timber washer / lag screw design, or a "collared lag stud," and it found a new use for supporting loads in live trees in the late 1990's. Arborist Jonathan Fairoaks, Michael Garnier, and Engineer Charlie Greenwood all had some amount of input into the original prototype that came to be known commonly known as the garnier limb or "GL." The garnier limb at that time was a fantastic accomplishment and a step in the right direction. The major shortcoming of the original garnier limb was the weak point behind the collar. This issue was subsequently addressed by pushing the threading to start back 2 inches behind the collar, and creating a conical stress transition point. Charley Greenwood further specified heat treating and other details on his STF (Stud Tree Fastener) diagram (he chose not to use garnier limb as the name at that time). Treehouse builder Dan Wright has modified the thread specs from the STF design to make them faster to install and do less damage to the wood on the way in. These are the current specs preferred by Treehouse Supplies for our Treehouse Attachment Bolts.
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