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For Bow Arms / T
1 1/4" T
2X 1 1/4" - 1" Bushings
1" PVC
3/4" CPVC
1/2" CPVC
Duct Tape

Front Plunger Rod  Assembly
1/4-20 Nylon Eyebolt
1/2" Nylon/Delrin Rod
1/4" Aluminum Rod
3/4" PVC Endcap or other catchpiece
1/4-20 Nylon Nuts

Plunger Head
Thick Rubber Washer
1/4" x 1.125"-ish Disc (Any thickness)
1/4" x .875" Disc (3/16" < x <3/8" Thick)
1/4" x 1.25"-ish Disc (Any thickness) 
Skirt Seal MC #9562K46
More Nylon Nuts

Rod Seal Assembly
3/4" Plug
3/4" T or other 3/4" coupler
1/4" x 3/8" Flanged Bronze Oilite Bushing
6-32 x 1/4" Screws

Plunger Tube / Frame is 1 1/4" PVC
1. Drill a 3/8" hole in the center of the plug.  

I used a lathe with a 1/4" drill to make the hole, then expanded it with a unibit to 3/8".  What matters is that you end up with a 3/8" hole, and that the hole is very close to the center.  If it seems a bit tight, try taking off a small amount of material with scissors.

2. Press the bushing into the hole, flange out.

3. Drill and tap two small threaded holes for retention screws.  I used 6-32 x 1/4" screws

4.  Install the screws.  Don't over-tighten them, as you can easily tilt the bushing with these screws.  It's better for the bushing to wobble around in place than be fixed to a crooked position.
5. Press (Or glue, if you're into the permanence thing) the plug into your T. 

 I used an unusual 3/4" coupler that I found at menards for a couple bucks.  A regular T will work fine, but has a bit more deadspace and puts more bend in the airflow.  You could use a regular coupler, or even a cap if you take the trouble to drill and seal a hole into the plunger tube.