Four Screw Pre Model 10 from 1957 - '58

[Old cop]

This may sound like a silly question but does anyone know the purpose of the screw in front of the trigger guard? I picked up a 4" in 85% condition and it is a great shooter and HD gun. I'd post pics but at my age, 65, am technically challenged.

Thanks,
Old Cop
LEO '68 - '97

[JAREDSHS]

the screw serves to hold the cylinder crane in the frame.

[H Richard]

The screw in Front of the trigger guard holds the spring and plunger that powers the cylinder stop.
This is a model marked Mod. 10 from Oct. 59, but it is still a 4 Screw.

[Old cop]

Thanks for your help!