Although I have shown you the Invincible before this one is supplied by Charles Smith of Deritend Bridge 'Works' Birmingham and later of 17 Conduit Street, London. Charles Smith and Sons were well known as contractors and manufacturers of all type of metal ware, supplying to many public buildings and mansions including Windsor Castle. They are however probably best known for their locks rather than the supply and manufacture of door checks.
It is interesting as this one had an adjustable spring which comprised of 3 springs (one inside the other), it being therefore more powerful than the previous Invincible's I have shown you. It should be seen that this model uses square section springs similar to many Robert Adams designed checks and closers.