We should really get a "Type C" sticky, since these are common questions and do require a bit of explanation.
The Type C does have a slightly different profile than a D, but to the casual eye it's a subtle difference. There's a slight "break" to the curve of the throat on a C, while the D has a smoother curve. (See the pic SP1Colt posted above to compare a C and D side by side). Once you've seen it and noticed it a few times, it becomes much easier to detect.
More noticeably, the Type C is narrower than later stocks. (For more detailed measurements, see my first post in
this thread.)
I also
believe most Type Cs had uncoated sling swivels. I've heard suggestions that some late ones had coated swivels, but the Type C's I've found with coated sling swivels have been of questionable provenance. I lean towards them having been replaced--but I cannot guarantee that.
The "straw hole" is a common misconception. Many people think if a stock has a hole, it's a D, but we've seen quite a few C's with straw holes. I believe they are later than the no-hole stocks and have noted two other things: Type C's with a drain hole are slightly thicker than Type C's without a hole (but still much thinner than the Type D); and the drain holes in Type Cs are not so carefully centered as the holes in Type Ds. (Again, see my link above for examples.)
OK, I've marked up this pic (from the auction in question) to illustrate the major changes.
From this angle, it's often easy to see the "break" in the throat curve.
Note the marked width of the stock (at the neck) is approximate. They do vary a bit.
And note that the straw hole is off center (typical).
And here's why the width of the stock matters (to those of us who care about details)...
I hope Billat10k doesn't mind my borrowing his pick from
his thread, but it shows a Type D stock. Note that the "rim" of the buffer tube is smaller in diameter than the stock (the stock is wider than the edge of the buffer tube).
In contrast to that Type D thickness, Type A, Type B and Type C stocks were all slightly
thinner than the width of the buffer tube (occasionally about the same width as the tube, but not wider).
Here's an "A" to compare:
I hope that helps people see the differences. It's important to know when a stock is worth the extra money!