Your brass triggerguard appears to be from a Colt "cap-&-ball" revolver, manufactured from the 1840s into the early 1870s. Precise measuring could reveal the specific caliber-model (.31, .36, 44-caliber) it is from. The serial number marked just in front of the guard can also be researched, via the Colt Firearms Company.
Hey Tigerdude; Found this one last year form a Colt 1849 Pocket Model 31 caliber, made in 1865 If you can let me know the distance from the front screw hole to one of the two rear screw holes center to center, we could most likely pinpoint the model. Then if the number is readable we can get you a year of manufacture.