Here is a recent article we wrote for PCGS on missing clad layer mint errors. We covered all the basic missing clad layer types, and give some additional information on rarity and collecting them. Here it the link to the article on PCGS' website:

https://www.pcgs.com/news/missing-clad-layer-mint-error-coins

We recently wrote this article for PCGS on strike thru errors. Here's a handy link: https://www.pcgs.com/news/the-two-types-of-struck-through-error-coins

Read our article on off-center strikes we wrote for PCGS on their website:

https://www.pcgs.com/news/the-popular-off-center-strike

Struck Through Errors

Building an Error Coin Collection

by Jon Sullivan

U.S. Coins on Argentina 10C Planchets

by Jon P. Sullivan

Split Planchet Jefferson Nickels

By. Jon P. Sullivan

Building An Error Type Set

by

Here is an excellent article on the subject, put out by NGC. It will describe in detail what they are, and how to detect them. http://www.ngccoin.com/news/viewarticle.aspx?IDArticle=4412&Wheel-Marks