The Museum of National Antiquities in Stockholm has entrusted the Nordic Museum with a padlock with double ward springs. When locked, the springs rest against a wall in the lock body with two notches that match a key with a double bit. The two curved bits press back the springs, releasing the shackle. The lock was a treasure found in the province of Uppland. It is made of wrought iron and is a technical predecessor of medieval spring padlocks, which have an arched swivel shackle and separate springs. The difference is the way the key works, and that the shackle of the Uppland lock is fused with the lock body.