The pipe thread area is a point of weakness and the overlap is way to short
to provide any strength. A better alternative is aluminum tubing with .058
wall thickness.

This allows decending sizes to fit with in one another. For example a 1"
6061 T6 10 foot long has an inside diameter of .884 and a 10 foot section of
7/8" (.875) will slide right into it. This would allow an overlap of almost
4 feet providing all the strength you need.

Good luck on your next installation.
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Ground system:

5 foot of 1 inch diameter galvanized iron pipe, halfway stuck in ground
with concrete.
1 inch diameter galvanized coupler
5 foot of 1 inch diameter galvanized pipe
1 inch to 3/4 inch copper reducer
1 foot of 3/4 inch copper pipe
4 tees: 3/4 inch thru vs 1/2 inch out, soldered lengthwise along
copper pipe.
an 8 foot length of 1/2 inch copper pipe soldered into each tee
tees are reinforced above and below radials with a hose clamp
coax shield connected to top of copper pipe

Radiator:
10 feet of 3/4 inch diameter copper pipe
9 foot carbon fiber fishing rod, handle epoxied and inserted into pipe
a wire is attached to copper pipe and run up to end of rod.
Hot end of coax connected to bottom of copper pipe

Ground system and Radiator are connected in-line with a PVC twist shaft
coupler designed for 3/4 inch pipe, weather sealed with epoxy. A gap
of 1 inch between pipes inside the coupler is filled with styrofoam to
prevent contact.

Rope guys are econnected to the top part of the shaft coupler, as the
middle of the shaft coupler is predicted to be weakest point.

Sure enough, a continuous wind in excess of 60 mph vibrated the shaft
coupler into 2 pieces despite the guys, the radiator then collided with
a radial, knocking a radial out of alignment and ripping apart a hose
clamp. I suspect the wind is going to finish the job overnight.

Sigh,

The Eternal Squire