I have a very nice 19-4, blued, and 4". It has RR, WO but I wanted TT and TH also. Bought the TT and TH from a very nice forum member thinking they are a drop in parts, needing maybe, very little fitting.

Wrong!

The part of the new trigger that lifts the new hammer, will not fit into the recess under the movable part on the hammer. Also the timing is off due to the cylinder stop not working correctly with the new trigger. I changed the parts over from one trigger to the other but I do not think this is a part of the issue.

I suppose I will take it to a local gunsmith and have him fix it up for me. By the way, I placed the .265 T and H in a 10-5 snub, it works great.

Learn something new every day!

I personally never had trouble fitting the hammers or triggers over the years - seems like it has gotten to be common to swap them since real target triggers are darn hard to find and my trigger finger must have one.

I am no expert like the other gents posting here

I have swapped several and all worked just fine except one. And that one all I needed to do was to adjust the trigger overtravel a smidge. But I have always gotten a matched pair that were together in another revolver.

Putting the sear ("the movable part on the hammer") from your old hammer on the new hammer frequently fixes that part of your problem.

That is it exactly. Pete