There are three different styles available so you need to know 3100's are unique: First picture shows 3100 with offset holes. 3600, 3800, 4000's and 6000's use the next picture. 5000 series COE have their own unique type. There are as many as 4 shims and two lock plates (threaded) which go inside behind seat tub. It is a good idea to use them instead of just nuts and flats since they will pull through depending on use.

http://good-times.webshots.com/photo/2235943390102454676FUuGUv
http://community.webshots.com/photo/2379203940102454676qNTFMD