will this spear tip fit a JBL D7 gun?
No, It won't fit the shaft.
The spear tip pictured here will rust. If the tip is claimed stainless, then it weeps...a lot. I used the 3601 only a short time and don't remember if it required an adapter.
JBL makes excellent tips. Since you are asking if the tip fits a JBL gun, I recommend the JBL single barb point, JBL stainless steel twin barb Rock Point 2 -5/8, or the JBL rotating tri cut point. You cannot beat JBL tips. The pin that holds the floppers is thicker than the Omer. The flopper material is thicker than most others. Last summer I lost a very large Cobia due to the flopper slipping off a small pin. If you hope to get large fish, JBL also makes slip-tips that work!! Most slip-tips slip off before you find a fish!! Good Luck! Have Fun! Be Safe!!