Porter, three threads, entire.

Porter first brewed by R Harwood at Shoreditch in 1722: a popular drink of the time was three threads, composed of a mixture drawn from 3 casks - troublesome for the publican. The new drink was "ready mixed", one beer with the properties of the mixture, and known as "entire butt" or just "entire". It soon became popular with London porters, and gained the name "porter".

The mixture of three threads is disputed, 1/3 pale ale, 1/3 brown, 1/3 old, or perhaps pale, new brown & stale brown, or pale, brown & small, or pale, strong & twopenny.

Paraphrased from Beer & Skittles; Richard Boston, copyright 1976