There were several different types of bicycles that were sold under the Roadmaster name. Your bicycle probably has a Ashtabula crank or what's commonly called a one piece crank. Where the left and right crankarms and spindle are the same piece of metal..

This link should help you.... https://www.sheldonbrown.com/opc.html

If it is a crankset that has crank arms that are removable from the spindle, then knowing a little more about the bike might help.

When asking for mechanical help, the best place for your thread will be the Bicycle Mechanics sub-forum.

Here is the picture you tried to post.




https://www.bikeforums.net/g/album/38070490

They upload to your album. Even though you can't post them in a thread until you have at least 10 posts or replies of your own here on BF.

A picture of your bike. Particularly the crankset and bottom bracket will be more helpful.

Welcome to BF.