What is the most common frequency shift for RTTY emissions in the amateur HF bands?

Radioteletype (RTTY) transmits data by rapidly shifting the carrier between two specific frequencies, known as the 'mark' and the 'space'. In amateur radio HF bands, the standard difference—or shift—between these two frequencies is 170 Hz. While other shifts like 425 Hz or 850 Hz have historically been used in commercial, maritime, or military communications, 170 Hz is the universal standard for amateur HF RTTY.