I'd say that's bacterial spot. Is it on the leaves as well?

Here is a link that might be useful: bacterial spot pictures

nothing on the leaves. this is on about 1/2 the peaches & all of the all of my nectarines.

Then it's scab. A fungicide (like captan) starting at about thumbnail fruit size will prevent the scarring. Just curious, what variety is the peach?

there are several varieties & they all have it. too late for this year but i'll know better next year.

I have had some chronic problems with scab on my peaches too, and have mistakenly thought that any fungicide would be effective. I found this very helpful paper on the website of the USDA station in Kearneysville WV (link below) which says that only captan and sulfur among the fungicides listed are effective vs peach scab, and that copper, Immunox (myclobutanil) and Daconil (Chlorothalonil) are not effective. The table 3.3a on page 6 is the source of that statement - however it does not mention Monterrey Fungi Fighter (Propiconazole), another antifungal agent.

Going to change my early spray schedule next year.

Here is a link that might be useful: Home orchard pest and disease management