Remington magazine cap retainer, Express 12 or 20ga
This device retains the magazine spring and the magazine cap on Express models. If you buggered yours up and the teeth are damaged you magazine cap could come loose. These are take offs out of the new 870's I build my custom models from. Retails for $4.37 on the Remington parts list. Choose either 12ga or 20ga from the drop down box.