I have partially assembled a tree bookcase and have discovered that I have been supplied with an incorrect part. I was supplied with the part shown in the attached picture. The pictured part is 76mm in length, yet the assembly requires the same but at 71mm. I have contacted the vendor, who do not know the part's name, but assure me that I can find them in any hardware store. No hardware store I have visited has been able to identify it, though.
Please, can somebody tell me what is the name of the part, and where can I find one that at 71mm?