The centre stand with the nuts on the shaft is the 1954 - 57 type. It has a shaft with a sleeve which bolts up tightly between the frame mounts. The stand rotates on the sleeve. I have found mostly that the sleeve wears and the stand is OK.
On post '57 bikes I use the cast stand as the fabricated ones used in 1958 - 59 are usually beyond repair. The frame lugs, stand and spindle are usually worn so I bush the frame and stand, make a new spindle and drill and tap the frame lugs to fit grub screws to stop the spindle moving in the lugs. This stops the frame from wearing and future repairs, if any, will only be rebushing the stand and new spindle.
These stand spindles were secured with split pins and washers and a thackery washer to stop rattles.
Trev.