Buy on Installments vs. Buy in Installments: What's the Difference?

'Buy sth. on installments' and 'buy sth. in installments' both mean the same thing: purchasing something with regular payments over time. The difference lies in the prepositions used, 'on' and 'in'. While there's no significant semantic difference, they convey a slightly different feel. Both phrases are widely accepted and interchangeable.