Observing moon

I was showing some friends the moon a couple of weeks ago, and Ive been curious myself, whats the smallest feature viewable on the moon? Like is there a small crater or some feature I can show that I can also say " this crater is this many miles wide"? Where do you guys get info like this?
I have a 4" Takahashi, and an 8" celestron.I often use a 4mm radian on the Tak which is around 200x.
Tony.

Davy and Davy Y. There is a craterlet chain that shows craterlets about 1/2 to 1 mile across. I have a drawing by Herring from 1959 Sky and Telescope but I do not know if it would be correct to post it here without permission.
L. Regira

Well I don't know what's the smallest feature, but short of the Rukl Atlas, you can get the info by installing this very useful free program.
http://astrosurf.com/avl/UK_index.html

There's also a new book about, which has finally put sanity into observing the moon for this lunartic newbie, "The Modern Modern, A Personal View" by Charles Wood.

Ron B[ee]

Hope this helps. This chart is from Muirden's "How to Use an Astronomical Telescope" -

Aperture.......Smallest Craterlet...Narrowest Cleft

25mm ....... 15 km............. 800m
50 ......... 7 ................ 400
75 ......... 5 ................ 270
100 ........ 3.5 .............. 200
150 ........ 2.5 .............. 140
200 ........ 1.8 .............. 100
250 ........ 1.5 .............. 80
300 ........ 1.2 .............. 70
400 ........ 0.9 .............. 50
500 ........ 0.75 .............. 40

These stats assume the object is near the terminator.

cheers,
Rob