For context: I am a project manager on a construction site. I am a woman. There is a fella that has come out to my site to repair a generator on a few occasions. We've only briefly spoken up until a few days ago. On this occasion, he came into the job trailer to discuss why the generator keeps throwing codes. While we were talking, I am 99% sure he caught me checking his left hand for a wedding band. (There wasn't one.) Almost immediately after, he officially introduced himself by giving me his name and told me where I could find his cell phone number. (It's on a sticker on the generator.) The conversation was animated and friendly, and I made a joke about intentionally sabotaging the generator so he would need to make another trip out.
I would like to text this fella to find out if he's single, and invite him on a coffee date. Am I crossing a professional boundary that I shouldn't? If a text seems like a sane and reasonable thing to do, what should the text say?