Appearance and effects
The Writer's Block is a large, heavy cube, presumably made out of wood. The idea is to place it one one's desk so one can't write there anymore. He presented it to Hobbes in its only appearance. When Hobbes dismisses the idea, Calvin laments that he must be years ahead of his time. The Writer's Block never appeared again.
The Writers Block is a pun on 'writers block', a phrase which means the author has run out of ideas(and so can't write).