I think they are threaded the same, but are slightly different sizes. I remember reading somewhere that the spyder cupseal is bigger, so it would need to be sanded down to the right size.
You might want to try calling Kingman (1-888-kingman), they might have what you are looking for. They had my safety and sight rail in stock.
But I don't know if I should be helpful, seeing as you are a Redskins fan...
You know, it's against the law in Baltimore to root for the Redskins.
2003 ICD BKO w/ 45/4.5k, Ricochet Apache
'98 r/f Autococker w/ 45/4.5k, J&J Edge kit (14"), Ricochet 2KX
PCS US-5 Mech. w/ 48/3k, J&J Edge kit (10"), cyclone feed, JCS folding voodoo stock with RVA
Kingman Hammer w/ 13/3k, J&J Edge kit (14")
Projects in the Works:
'99 r/f Autococker w/ 45/4.5k, J&J Edge kit (14"), and THE CYCLONE!!!