M1 Thumb/Garand Thumb refers to an injury sustained by the operator of an M1 Garand rifle in the process of pushing the en-bloc clip down until it engages. It is caused when the bolt stop slips out of engagement, allowing the bolt to slam forward with the operator's thumb still in the clip/mag well. This causes the thumb to be trapped and can sometimes require moderate medical attention to treat, such as stitches, depending on the angle and strength of the bolt as it hits the thumb.
