This is a replacement trapdoor spring plunger for the Phrame 1.0 and Phrame 75. 
 
This plunger does NOT have a nylon locking patch, mking it easier to install than the initial run, but requiring Loctite 243 or similar to help retain it in position. 
 
Install it so the ball is slightly proud of the bottom of the Phrame, but the threaded body is recessed into the hole. If the body protrudes, it will scratch the trapdoor and create drag. I install them intentionally "too deep", then back them out until just right. A 3/16" bit in a powered screwdriver on low speed is best. 
 
McMaster PN 3408A71