Correct Neck Pegs

Hello!! New Guy here...I'm currently working on a mod that requires a head swap but I've run into a small problem. I've found out that Hot Toys uses at least 3 different neck pegs. I've tried the longest but it does not fit what I'm trying to accomplish. I believe I need the medium size peg in this pic but I'm not sure what figure to get it from. Can anyone help me with this issue?? I apologize in advance if this thread has been posted already. Thanks a bunch!!