To determine your PS2 version, here is a simple guideline according to its model numbers and serial numbers.

Hint: You can find a PS2 model number on its blue box or look at the sticker on the back. If your PS2's model number is SCPH 3000x (x determines a number, ie. 30001 for US PS2, 30002 for Australia and NZ, 30003 for Europe PS2, 30004 for UK PS2).

USA PS2 MODEL NUMBERS
30001 v1-3 = 10 Screws on base of the PS2.
30001 v4 = 8 Screws on base of the PS2 and an Electrical Hazard Warning.
30001R v4 = 8 Screws on base of PS2 and an Electrical Hazard Warning.
30001R v5 = Same as above with an extra screw on the top of the Expansion Bay.

USA PS2 SERIAL NUMBERS
U1 : version 1 with 10 screws
U0 : version 2 with 10 screws
U0 : version 4 with 8 screws
U2 : version 3 with 10 screws
U3/U4/U5/U6 = version 4 with 8 screws

AUSTRALIA/EUROPE/UNITED KINGDOM PS2 MODEL NUMBER
30002/3/4 v3 = 10 Screws on base of the PS2.
30002/3/4 v4 = 8 Screws on base of the PS2 and an Electrical Hazard Warning.
30002R/3R/4R v4 = 8 Screws on base of PS2 and an Electrical Hazard Warning.
30002R/3R/4R v5 = Same as above with an extra screw on the top of the Expansion Bay.