I just played around with replacing the o-ring on a spare inflator hose. I used a machine screw with a narrow head and I took apart a Bic pen and used the short plastic tapered piece between the roller ball and the long tube of the pen. Bic pens pull apart easily and then you just push the whole ink tube and roller ball head out.
Here are the steps I used:
1. Put the machine screw in the inflator with the screw head down against the schreader valve.
2. Put a size 011 o-ring over the end of the machine screw and push it into the opening of the of the inflator hose.
3. Use the non-tapered side of the short collar tube from the Bic pen and slidd it over the machine screw to gently push the o-ring down into place. Use short up and down movements to slowly work the o-ring down into position. The o-ring will sort of snap/pop into place.
4. Remove the pen piece and the machine screw and take a quick look into the end of the inflator to double check that the o-ring is properly seated.
It took me longer to insert the o-ring into the end of the hose than it did to use my homemade tool to properly seat the o-ring in its groove. All in all it took less than a minute to install the o-ring.
The nice thing about using the pen piece is that I was able to reassemble the pen for continued use. I have now added a Bic pen and machine screw to my save-a-dive kit and swapped out the clicker type ball point pen in my dive log for a Bic pen.
I just realized that Bic makes a bunch of different stye pens. Here is a photo of the type I used. The piece I refered to above is the tapered colored collar between the end of the white section and the tan/brown writing tip. the white tube is just a tad too big to fit into the inflator hose end.
-Z