The two tonearms are very similar but are not identical. Jelco manufactured all of the Audioquest PT6 tonearms. Also the Audioquest tonearms are discontinued so that SA-250ST may have some design improvements.
Here is the information on the Audioquest PT6 and Jelco SA-250ST.
Audioquest PT6
Jelco SA-250ST
Effective length: 229mm (Audioquest), 228mm (Jelco)
Overhang: 18mm (Audioquest), 18mm (Jelco)
Mounting distance: 211mm (Audioquest), 22108mm (Jelco)
Mounting pattern: Linn type (both)
Posted in: Jelco Tonearms and Accessories