I just got 188 of these fire bricks for $75. They measure 4" x 4" x 11.5". They were unused liner bricks for a steel foundry. They have no name just the following: " l5l17 ". Each weighs 10.4 lbs.
Has anyone seen this type of brick before? Some of the tongue and groove bricks I see on the internet are made to withstand cone 32?