But... "So do you want _a_ specific thing, or will any thing work?" sounds kind of correct as well to me. (Disclaimer: I am not native speaker, grain of salt and all.)
But... "So do you want _a_ specific thing, or will any thing work?" sounds kind of correct as well to me. (Disclaimer: I am not native speaker, grain of salt and all.)
It is. Yours is acknowledging that your things are distinguishable and the other person might want one in particular.
GP's should be used when offering a specific one, like "the red one".