KPSI stands for Knots Per Square Inch. In hand-knotted carpets, this term literally refers to how many knots can be counted in a square inch of carpeting. As a general rule of thumb, rugs with a higher KPSI are better quality than rugs with a lower KPSI. However, to truly use KPSI to your greatest advantage, you must only compare apples to apples. Only comparable rugs (rugs from the same country, city, style, etc.) should be looked at when comparing KPSI, as sometimes a higher knot count is not necessarily the result of a better quality rug, but rather the result of a low quality, thinner wool. Also, some rugs are just always going to coarser than others (geometric vs. floral styles, for example).

I'm not sure if your referring to 400C or 400F.

But, according to Shigley's Mechanical Engineering Design, 8th edition by Budynas and Nisbett.

The tensile strength of 1050 steel quenched and tempered at 400F (205C) is 1120 MPa (163 kpsi).

The tensile strength of 1050 steel quenched and tempered at 425C (800F) is 1090 MPa (158 kpsi).

1/4" Lexan weighs 1.56 lbs per square foot

Stainless Steel 316 properties -

Tensile Yield Strength (.2% offset):

276 MPa / 40 kpsi

Ultimate Tensile Strength:

621 MPa / 90 kpsi

Not sure which you're looking for, so both in case. Yield strength uses the slope of the initial elastic region of the stress-strain graph to determine a 0.2% offset along the curve; ultimate tensile strength is essentially the maximum stress experienced along the stress-strain curve.