Three point bend testing fixtures use center loading to flex the sample. Common 3 point bend tests include ASTM D790 for plastics, and ASTM D143 for wood. The 3rd point loading nose is attached directly to the top arm of the universal testing machine by use of a clevis pin adapter. The bottom two supports are adjustable and can accomodate samples of different length. The concentric gear crank custom bend fixture is a nice solution if you are changing between multiple specimen sizes.