Hi
Both are very nice knives. I gave a past girlfriend a 640S for an anniversary one year, it became her most favorite thing in the world, never ever went anywhere without it. Below is a picture of the 650S, and I know I have a picture of the 640S just can't find it.
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<img src="http://www.crimsonhorizon.com/graphics/bladeforums/bm650s-l.jpg" align=center valign=middle border=0>
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<img src="http://www.crimsonhorizon.com/graphics/bladeforums/bm650s-r.jpg" align=center valign=middle border=0>
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<b>Blade Length:</b> 4.1"<br>
<b>Blade Thickness:</b> 0.125"<br>
<b>Blade Material:</b> ATS-34 stainless<br>
<b>Blade Style:</b> Satin Finish, Combo Edge<br>
<b>Overall Length:</b> 9.33"<br>
<b>Sized Closed:</b> 5.23"<br>
<b>Handle Material:</b> 6061 T-6 Aluminum<br>
<b>Weight:</b> 4.2oz.
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