Sonora Mechanism question

[Franklinp40]

Hello everyone. I just picked up a Sonora phonograph from the neighbor. I have a bunch of old records i bought for a dollar so I thought i would try to play them. The part (hopefully) pictured below was lying in the cover. I pretty guessed it has something to do with stopping the spring barrel from spinning so it can store energy. I cannot figure out how to put it back. Any one have a picture of this part installed properly? Thank you so much in advance.