On Wednesday, August 22, 2018 at 2:44:30 PM UTC-4, Clare wrote:
It's in a joist pree drilled
https://www.homeownershub.com/img/fz
https://www.homeownershub.com/img/g0

I would not rely on on a lag screw, especially where it could spin/rotate. I put a pair of 2x4's with 1/2" plywood spacers across 2 joists (attic) and used a threaded eye bolt/locknut and a 3/4" plywood "washer" to hang a similar chair, and likewise on a "floating" corner of a loft bed, rather than a corner post to the floor...