First of all, I would like to thank you all for all the valuable information on this site. I've used it to build my first AR-15.  So I feel I owe you guys this.

The instructions for my Jewel Trigger required dry firing a bunch of times to get the trigger set up.  They tell you to protect the receiver from the blow of the hammer, but don't really tell you how. So, I got my dial calipers out, made a sketch, and took it into work.  I found a chunk of plastic in a scrap hopper that was almost perfect size, so that’s what I used. But I'm sure you can use anything, aluminum, steel, wood.  Anyway, this is what I made:
http://i43.photobucket.com/albums/e359/dirtrunner_22/AR-HammerBlockRemoved.jpg

First I drew these dimentions on the side of the plastic, and cut it out with a bandsaw.
http://i43.photobucket.com/albums/e359/dirtrunner_22/AR-HammerBlockDemensionsSide.jpg

Then I put it in a vertical milling machine to cut the thickness and the slot (in black) for the bolt catch.
http://i43.photobucket.com/albums/e359/dirtrunner_22/AR-HammerBlockDemensionsBottom.jpg

Here it is installed in my lower. It works pretty slick.
http://i43.photobucket.com/albums/e359/dirtrunner_22/AR-HammerBlockInstalled.jpg

I know not every one has access to a milling machine, so I would recomend looking for something that is aready .875" (7/8") thick.  Then you can use a grinder to put the bolt catch groove in, which doesn't take much.   I hope this helps someone out.   I think its perfect.   I carry it in my case for any trigger set up I might encounter at the range.   Happy Shootin!

good post.  i made my first one after breaking my bolt catch.  i wish i made mine longer like yours so i could clamp it on the bottom in a vise.

bump for a good thread!  

DO i hear dollar signs????  LOL