Taken from
http://psxpaul.cjb.net
[AUS/EU/UK] PS2 PAL
30002/3/4 v1-3 = 10 Screws on base of PS2
30002/3/4 v4 = 8 Screws on base of PS2
30002R/3R/4R v4 = 8 Screws on base of PS2 & 2 screws in upper rim of expansion bay
30002R/3R/4R v5/v6 = 8 Screws on base of PS2 & 3 screws in upper rim of expansion bay
39002/3/4 v7 = 8 Screws on base of PS2 & 3 screws in upper rim of expansion bay
[USA] PS2 NTSC
30001 v1-3 = 10 Screws on base of PS2
30001 v4 = 8 Screws on base of PS2
35001 v4 = 8 Screws on base of PS2 Serial # U5*** & U6***, Datecode 1B, 1C
30001R v4 = 8 Screws on base of PS2
30001R v5.x = 8 Screws on base of PS2 with three screws in top rim of expansion bay
39001 v7 = 8 screws on base of PS2