Ubalda, All Naked and Warm (1972) on Netflix

During the Middle Ages, a clumsy knight returns home where his wife awaits him. Sensuous and beautiful, she has attracted several male admirers during his absence, but her chastity belt has maintained her faithfulness. Now is her chance to wrest the key from him and enjoy herself. The knight's portly friend has a similar problem with his equally gorgeous wife. And to top it off, both men have designs on the other's wife -- leading them to devise painful methods to discourage the other from trespassing.

—GoblinHairedGuy