I had this same problem. You need to put in the lengths exactly. Here is a list I found on Nelson Stud Welding website. Try putting in 5 5/16" instead of 5 1/8" for the 1/2" H4L. Its weird, 5 1/4 wont work, 5 5/16 will, 5 3/8 won't. I printed this out and put it in my Advance Steel notes. Ron
H4L 1/2 X 3 1/8 MS
H4L 1/2 X 4 1/8 MS
H4L 1/2 X 5 5/16 MS
H4L 1/2 X 6 1/8 MS
H4L 1/2 X 8 1/8 MS
H4L 5/8 X 2 11/16 MS
H4L 5/8 X 4 3/16 MS
H4L 5/8 X 6 9/16 MS
H4L 5/8 X 8 3/16 MS
H4L 1/4 X 2 11/16 MS
H4L 3/8 X 3 1/8 MS
H4L 3/8 X 4 1/8 MS
H4L 3/8 X 6 1/8 MS
H4L 1/2 X 2 1/8 MS
H4L 1/2 X 2 5/8 MS
H4L 3/8 X 1 5/8 MS
H4L 3/8 X 1 3/8 MS
H4L 1/2 X 3 5/8 MS
S3L 3/4 X 3 3/16 MS
S3L 3/4 X 4 3/16 MS
S3L 3/4 X 5 3/16 MS
S3L 3/4 X 6 3/16 MS
S3L 3/4 X 7 3/16 MS
S3L 3/4 X 8 3/16 MS
S3L 7/8 X 3 11/16 MS
S3L 7/8 X 4 3/16 MS
S3L 7/8 X 5 3/16 MS
S3L 7/8 X 6 3/16 MS
S3L 7/8 X 7 3/16 MS
S3L 7/8 X 8 3/16 MS
S3L 3/4 X 10 3/16 MS A
S3L 3/4 X 2 3/16 MS
S3L 3/4 X 4 3/8 MS
S3L 3/4 X 3 7/8 MS
S3L 3/4 X 4 7/8 MS
S3L 3/4 X 3 3/8 MS
S3L 3/4 X 5 7/8 MS
S3L 3/4 X 5 3/8 MS
S3L 1 X 6 1/4 MS