was surfing around and found these lens

310x310, focal length are: 326/220, 2 lens stuck together apparently

would those be useful for diy lcd projector?

Sounds like they would be useful if you were to use them in an unsplit configuration.

are these the ones from 3dlens? Sound like the same specs as A395a and A395b or 310a and 310b
http://www.3dlens.com/enter.html
click on shop online and then on large fresnel lense

By the way they have a new lense for sale
320mm x 400mm
Item: #F550
Thickness: 1.5mm
Weight: 280 grams
Material: optical acrylic
Groove pitch: 0.2mm
Focal length: 550mm
Might this be of use for the 17" + models?

yes, it is for long throw projection lenses. (somewhere 450mm focal)