Final answer:
The correct answer to the question is 'safety pin,' which is a crucial safety feature for securing attachments on pneumatic tools to prevent them from being ejected during use.
Step-by-step explanation:
When using pneumatic tools, a safety pin must be installed to prevent attachments from being ejected during tool operation. The safety pin is an essential safety feature that secures the tool's attachments, ensuring they remain in place even if there is a sudden increase in air pressure or the tool is dropped. With the use of a safety pin, the risk of injury or damage from flying attachments is significantly minimized, enhancing the overall safety of pneumatic tool operation.