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).