All of these parts are interchangeable and fit the .177 and .22 barrels listed. The bolt caliber must match the caliber of the barrel.
In the main photo, the top one is a Discovery breech. It fits 1740, 2240, 2250, 1760, 2260, all 2300 models and 2400KT. It has a full scope rail which makes it the best fit for scope rings and Williams notch and peep sights. The middle one is the same long breech available with Custom Shop models. It fits the same models as the Discovery breech but has a notch for mounting the Crosman LPA rear sight. Both of these breeches require a notched striker to allow clearance for the inner breech screw. That screw is under the bolt where it doesn't interfere with the pellet sliding forward. To access the inner breech screw, these breeches need to be installed with the end-cap removed from the tube and the bolt handle off.
The bottom breech is the standard one available with the Crosman Steel Breech Kits 1377SBPK & 2240SBPK. It fits standard Crosman 13XX & 22XX models but will not fit Discovery or Maximus models due to the inner breech-screw position. It works with standard and notched strikers and is the easiest one to install. It has a notch for mounting the Crosman LPA rear sight. This is the only steel breech I have listed that fits pump models 1377C, P1377, PC77, 1322C, P1322, 2289G Backpacker and 1300KT.
All three breeches require a 3/4" long rear breech screw. The 13/16" screws that are standard on plastic breech models are too long for a steel breech. Too long of a screw will damage the striker spring, spring guide and/or power adjuster.
The standard rear sight used with plastic breech models does not fit any of these breeches.
The steel plug is standard for all three breeches.
The top two bolts are .22 caliber, the bottom two are .177. Both calibers have long-nose and short-nose versions. The black short-nose and long-nose bolts are steel with black-oxide finish. The other long-nose bolts are stainless steel. The .177 stainless version has a magnet in the back that holds it open while loading. The black handles are steel with black oxide finish, the other long handle is nickel-plated steel. The long-nose bolts push the pellet further past the barrel port which creates a better seal between the pellet and barrel. This produces more consistent velocity and tighter shot groups. The short bolts tend to work better with extra-long pellets allowing more room to load them. The long handle fits better with wide scope rings and Williams sights. The short handles are more compact and tend to fit better in a gun case.
I suggest putting a small amount of medium strength threadlocker on the handle threads before attaching it so it doesn't tend to come loose but can still be removed with a wrench if needed. Tighten the handle finger tight only, the threads can be damaged if tightened with a wrench.