Danny D. wrote:
DecadentLinuxUserNumeroUno wrote, on Mon, 16 Feb 2015 19:24:43 +0000:

Drill a big hole through it, and put a stainless bar through the hole.
Voila! Attachment pins!

Right now, the two 16-foot boards to the side of the tree are unattached
at the tree (they're screwed into the floating bridge only).
https://c1.staticflickr.com/9/8566/1...37d554c5_c.jpg

At the moment, the bridge is wholly supported by the cables and, at the
low end, by the posts we first cemented into the ground, when we started
this project in the untrampled woods.

It is time for those attachment pins you speak of though...

What we are thinking is that they sell these $100 treehouse attachment
bolts, designed specifically for trees (but they're expensive since
we'd use probably use four or six of them overall).
http://www.treehousesupplies.com/Tre...Bolts_s/41.htm

We can't find anything larger than one-inch wide bolts at our local
Home Depot, so, we have to order our bolts online, at any measure.

We're debating right now the feasibility of 1 inch or 2 inch bolts,
which are about twenty bucks each, versus the treehouse attachment
bolts which are five times as expensive.
http://treehouseparts.mybigcommerce....2-36-hardness/

So, that's our next question. What kind of bolts make the most sense,
keeping cost in the equation (if cost were no object, the treehouse
bolts would do quite well).

I don't know what kind of bolt you will use, but here is my experience
with bolts in a living tree: I fastened some wooden squirrel feeders
to trees using lag bolts and washers. In a year the tree grew AROUND
the bolt, pulling it through the plank of the feeder. I learned to
put a spring between the bolt head and the washer to allow for this.

A threaded SS bar through the tree might be a better option, making it
longer than needed so you could back off the nut as the tree grows.
Of course you would want a jam nut so that it would not back off by
itself.

--
 GW Ross 

 I am a mental tourist. My mind 
 wanders.