The 821-424 is the ball-joint saddle for 1.67" (1-1/2" Schedule 40) pipe handrail: pivoting in multiple planes, it follows a curved corridor, a spiral stair return, or a rail that changes angle mid-run — geometry a single-axis swivel can't track. Both finishes, 316 polished and 316 satin, are rated for indoor and outdoor installs. It holds the rail at a 2-3/8" projection, fits .080" Schedule 40 wall, and fastens with two 1/4-20 stainless screws on the A114 companion tube. The same ball joint is offered at 1.5" and 2" if a run mixes rail sizes.