I read in "The AR-15 Complete Assy Buide" by Huleck & McKee that the use of this tool makes installing the pivot pin simple. Problem is I can't find anybody selling them ! Where can I buy one ?

Brownell's

just take a piece of bar stock close to same size of pivot pin hole, than drill a hole same size as spring an detint. it should show u how to do it but ill tell ya anyway.   Line up holes, put spring and detint in pushing with a small punch.  Turn the bar stock so spring/detint stays in receiver.  Slide the bar stock out while sliding the pin in.  there ya go.  It sounds difficult but its really very simple.   If you cant figure a way to make the tool i could prolly get you one.  just let me know.  [email protected]  

Well you're absolutely right. I looked but didn't look close enough. All I saw was the complete tool set for $795 didn't see that you could purchase individual components. THANKS!

Home Depot, it's called a clevis pin :) All kidding aside, I had the same problem. I needed a install tool and did not want to wait to get one. Read this post http://www.ar15.com/forums/topic.html?b=3&f=4&t=174996
This will tell you what you need. Don't waste your money on a pivit pin install tool. Thanks Big-Bore :)

Here's the link:

[url]http://www.ar15.com/forums/topic.html?b=3&f=4&t=174996[/url]

Use a razor blade to depress the detent and slide the pin in.

I had a 1/4" brass drift in my tool box.  Chucked it in the lathe and applied some 220 grit paper just so the drift fit into the receiver pivot holes.  Then, I drilled a cross hole a little bigger than the detent parts near the end of the drift.  Works great.  The tool need not be made of steel.
-WhiteFox

I build guns all the time and have never seen the need for a specific tool.

I use an appropriate sized Allen wrench run through the opposite side, to he edge of the pin hole.

Insert the spring.

Use a pair of needle nose pliers to insert the detent, then use a medium flat bladed screw driver to push it all the way in the hole and hold it there.  Push the Allen wrench through, sliding the blade off as it comes through.  Now the detent is captured.

Take the take down pin, provide rearward pressure and slowly slide the Allen wrench back through the hole . . . making sure the detent doesn't pop out on the way.

It's really easier to do then to explain.

I have shot a dentent on occasion, but I have yet to lose one

I used feeler gauge for automobile.  It worked great!  You can try different thinkness of the gauge until you find the correct one.