What is the standard rear sigh blade height on N frames?? I have a 625 that needs a new one, and .146" looks to be the most common. Thanks in advance..

Kind of depends upon caliber and barrel length. The heights are 0.126, 0.146 and 0.166. There's a 2 post thread on front sight heights where I gave the part numbers for all the variants, do a search-should be in the gun smithing section.