The Parker 51 Mk. lV Custom, introduced in 1971, featured a Gold filled cap, cap stud, and clutch ring. It was the last of the Parker 51 line, not counting the 2021 cartridge filled 'tribute' pen.
The pen is in excellent condition, it has a deep shine, clear ink sac, and totally ding and scratch free cap.
The cap is stamped:
'Parker 51. 1/10 12K G.F. Cap.
Made in U.S.A.'
meaning that the cap is 1/10th by weight 12Ct. Gold. the fine engraved longitudinal lines are still crisp and sharp.
Although the pen appears to have seen very little use, it was serviced and tested. The 14 Ct. Gold nib writes with a smooth, firm, fine line, ideal for someone with a small 'hand' or for detailed work.
The 'Rage Red' colour was only introduced in 1969, it is much brighter than the earlier 'reds' and is, by far, the hardest colour to find in the later Parker 51s. The colour was also resurrected in 2021 for the 'New Parker 51' cartridge filling pens. When referring to this pen as a 'later' 51 it should be noted that, at around 50 years old, it is still very much a vintage fountain pen, albeit the last of its kind.