I don't have any doubt about the bolt itself, and it would likely hold
200 lb in tension on a 3/8" lag bolt (that's essentially an eyebolt),
but I'd first be concerned of the span of the 2x4 rafter (or lower
truss chord). I'd not trust it as a mounting technique if I were
hanging from it or underneath a suspended load, though.

If I were doing somethng similar, I'd go _through_ (or even better
over) the rafter w/ a 3/8" bolt and a couple pieces of strap iron and
go through the bottom ends w/ a second bolt for the chain mount. AFTER
verifying what the actual 2x4 structure looks like--

I'd consider what you're suggesting for half the load if the load
weren't me or there were nobody ever under it, but it's definitely not
adequate safety margin in my view for the stated purpose (even w/o
looking up actual values). (Your numbers don't account for any dynamic
loading, for example.)


dph........ All good points and I certainly appreciate it. Might be iffy
for sure. Will see what others have to say too. Thanks again!