Callaham's Virtual Pop-In arms. These arms are designed for use only with Callaham's Enhanced Vintage blocks. This includes all of the Callaham trem products we sell:
"Enhanced Vintage" refers to the fact that Callaham inserts a Delrin sleeve into the block's arm hole, which mitigates any play in the threads, resulting in a better trem feel. These pop-in arms are designed for use only in these blocks, they are not appropriate for use with Fender blocks. Use Callaham's fully-threaded arms for Fender blocks.