Can't be certain on the W123, but the W126 uses 46mm. 1 13/16 would also be fine, but, it's only available in 3/4" drive. Due to space limitations, you can't use an adaptor on the W126 to get it down to 1/2".

I understand that there is a special short socket from M/B with 1/2" drive that is the proper tool for the job. Wish I had one.