The little clippie was most likely a spot (resistance) weld.
One good thing to do when trying to avoid penetration with GTAW is to clamp a copper piece directly behind your weld area, this heat sink will absorb extra heat and physically stop penetration from pushing thru into areas you don't want it. If you don't have copper, brass is good and even mild steel will work if it has sufficient mass not to melt when the heat gets to it. The most important thing is to have that heat sink directly pressed against the the work, a flush solid contact will draw a surprising amount of heat.
Secondly. a 0.040 tungsten with a long slim taper will reduce pentetration by creating a more bell shaped arc.
Clean everything to bright metal, 120 grit and scotch brite followed by Acetone/alchohol wipe right before you weld.
If you clamp your part to be welded tightly against the parent material and have a good heat sink behind them both you can probably get a nice fusion weld (no filler) to hold that part in place. Keep a little filler handy just in case things arent perfect.
If we were going into production, welding hundreds of clippies onto gun things, we could talk about pulse parameters, but without doing some trials on same/similar material I don't want to risk it.