The small screws in the circle are for secure and accurate fastening. Watching the video will help understand the process: first, loosen those three small screws fully, then use a pipe wrench to adjust and clamp the pipe as usual. Next, tighten the three small screws so their heads all press against the pipe surface. The third step is to release the pipe wrench, slide it along the pipe, and insert another pipe of the same diameter into the three small screw holes, aligning it with the original pipe opening. Finally, clamp the pipe wrench firmly to weld the joint between the two pipes.