Rare Primo Casket 1" quill mid / old school BMX stem.   Stamped 98.  3 bolts work well, 1 bolt has the correct threads, bolt head is larger than the cap hole, bolt would work if the head was filed down.  

Potts mod bolt. 

Primo Casket Stem Neck Old School BMX 1 in Threaded Quill CRMO Blue 4 Bolt 98