colt patent firearms
pt (patent) fa (firearms) mfg (manufacturer)
100-1000 USD depending on specifics
I believe 'pt' stands for patent, as in Colt patent firearms
You need a professional appraisal
You will have to provide caliber and ALL markings.
Impossible to answer without knowing the model, caliber and condition.
Colt
Depends on the model, age, condition.
Patent Firearms PT and FA (as used by Colt)
made about 1918
Colt............................
mfg. about 1875