Picatinny Rails question

[roysha]

I ran into a situation the last couple of weeks that still is not clear to me. Perhaps someone here can explain it to me. I have a DPMS AR with the flat top upper. I ordered a 1" and a 3/4" riser from, ultimately 4 different vendors, on ebay. Now before somebody starts on the ebay rant, forget, I'm not interested.

Here is the situation. All three were too wide by .020" to clamp onto the upper rail. I checked MIL spec. and it is .835 +/- a tiny bit. My DPMS rail measures almost exactly .832". Risers I received from the first three vendors were .852" +/-. I tried them on two Rock River uppers and a low single rail gas block with the exact same results. All the vendors corrected the transaction and the 4th one actually fit.

The first time I just figured it was an error in manufacture. Returned it for a refund and tried another vendor. Same thing. Figured 3rd time had to be a charm. HA! Same thing. Contacted the 4th vendor and asked them to measure the rail. It was correct. Ordered it.

One of the vendors said there was two different sizes of Picatinny rails and the larger size was what his riser was made for. Is this true? I have never heard of such a thing and I was under the impression that the reason for the Picatinny design was to eliminate confusing situations such as this. Am I wrong?

[tomme boy]

There is one size. The risors are made in China, what do you expect.

[scb]

These dimensions are correct. They look like scans from the gov't publication. There is only one.

http://en.wikipedia.org/wiki/File:M1913A_Rail_CrossSection.svg
http://en.wikipedia.org/wiki/File:Picantinny-recoilgroove-diagram.gif
http://en.wikipedia.org/wiki/Picatinny_rail

[roysha]

There is one size. The risors are made in China, what do you expect.

Profound!

[ilcop22]

There can be only one Mil-STD-1913. No rant necessary because it seems you already know that eBay is a horrible, horrible place to buy anything.