Convert ISTP to socionics
Your four letters are ISTP
About eight minutes.
ISTP does not convert to one socionics type, so this quiz decides between the three it can be: ISTp, ISTj and ESTp. The 20 questions are chosen for your four letters and ask about the places those candidates actually differ, not the places the letters already agree.
ISTP starts on ISTp here, though the letter-flip rule gives ISTj. The test's starting weights set the order.
Socionics writes the last letter small. It's not your MBTI letter.