I can't seem to find these anymore locally.  They are a great compromise between durability,  toughness and comfort.  Locally the stores only sell lighter weight "work pants" made by Dickies and other makers.  I'm not sure what type of "work"  they are designed for, but they all wear out quickly.  I thought Dickies didn't make these thicker ones anymore, but happy to find them on Amazon.  These don't rip if you catch them on something, and the knee lasts a long time it you kneel a lot on gravel and concrete.  Even my favorite jeans (I guess we can't use other manufacturer names in reviews) don't seem as tough as when I was young.