The history of 'wrot' as a variant of 'wrought'
A number of nineteenth-century texts use the contraction wro't or the abbreviation wrot. for wrought in tabular lists and equations to save space.
For example, a "Schedule of Manufactures, Buildings, &c., Materials used, Manufactures, Markets, Workmen, Wages" submitted in 1832 and printed in Documents Relative to the Manufacture of the United States, volume 1 (1833), includes tabular entries for the "1,500 lbs. wro't iron," "2,500 lbs English wro't iron, at 4 cts," and "2,300 lbs English wro't iron, at 4 cts."
And a list of "Premiums for Fancy Articles at the Annual Show" in Plymouth County, Massachusetts, published in New-England Farmer, and Horticultural Register (November 19, 1845) includes tabular entries for (among other things) "wro't slippers," "wro't bag," "wro't card-box," "wro't chair cushion," "wro't collar," and "wro't cravate."
Similarly, Thomas Dixon, Treatise on the Arrangement, Application, and Use of Slide Rules, second edition (1881) presents an arithmetical equation "giving the weight of Wrot. Iron Plate."
At least as early as 1869, the spelling wrot appears without an included apostrophe or period. From Agricultural Society of New South Wales, "Metropolitan Intercolonial Exhibition, 4th, 5th, and 6th May, 1869, Catalogue" (1869):
W. G. Ainsworth's list of exhibits, Ransome and Sims' make : BFO—1-wheel pony ; BFE—1-wheel 1 horse ditto ; BFEW—1-wheel 1 horse wrot frame plow, with steel mould board ridging body for above ; BFS—1-wheel light 2 horse plough ; BESW—1-wheel light 2 horse wrot frame plough with steel mould board ; YOHW—1-wheel 2 horse wrot frame plough, with steel mould board ; ...
Altogether this page contains 25 instances of wrot, despite using such unsimplified spellings as mould and plough, suggesting that people in Sydney in 1869 considered wrot a legitimate spelling.
Likewise from a table of measurements for Dartmoor Prison from the 1876 governor's report, in Report of the Directors of Convict Prisons ... for the Year 1876 (1877), we find entries for such items as these:
1" deal wrot, ploughed, tongued and glued in seats and risers for w.c.
1" deal facia, wrot, beaded and fixed
Making 1" ledged doors, wrot
1¼" deal treads and risers, wrot, glued, blocked and 3 fir carriages
Fir, wrot, framed, and chamfered in plates and posts
And from a table of expenses for "Modification of Tower" in Louisville [Kentucky] Water Company, "Eighteenth Annual Report of the President and Directors to the Stockholders" (1876):
25 wrot floor stays, 26 inches diam., 199 lbs. at 8.7 cents
7 wrot floor stays, 20 inches diam., 47 ibs. at 8.7 cents
15 wrot floor stays, 15 inches diam., 79 lbs. at 12% cents
759 wrot washers
One wrot-iron buoy
Wrot-iron guide for same, 455 lbs. at 12 cents
It thus appears that wrot was in use as a variant spelling of wrought in Australia, Great Britain, and the United States by 1876.
The status of 'wrot' today
A Google Books search finds a couple of books published in 1987 that use the spelling wrot in labels accompanying line drawings of various plumbing fittings: James Kittle, Home Plumbing Made Easy: An Illustrated Manual and William Cooper,Commercial, Industrial, and Institutional Refrigeration. Not to assume anything about TAB Books and Prentice-Hall, the fine publishers of these two books, but I know from personal experience that certain publishers sometimes use labeled public-domain (that is, free) illustrations that may be quite old and may not reflect current spelling conventions. The labels in these two books appear to be in the same font and format, suggesting that the authors cut and pasted the labeled illustrations from the same source. I haven't been able to identify that source, however
But those two books are not alone in mentioning "wrot copper." John Stephenson, Building Regulations Explained, sixth edition (2003) alludes to regulations governing materials suitable for use as rainwater gutters and pipes from a 1960 publication titled "Wrot copper and wrot zinc rainwater goods." Similarly, American Export Register 1994, volume 2 (1994) contains advertisements that mention "Wrot Copper & Cast Fittings" and "Wrot Copper Fittings"; and Plumbing Engineer, volume 22 includes the following item:
Wrot copper fittings
NIBCO's new brochure highlights the features of the latest additions to the line of wrot copper fittings. New sizes include 5- through 8- inch diameter fittings. They are made from pure copper mill products—ASTM specifications B75 Alloy C12200.
As for "wrot iron" that term continues to pop up in publications from recent decades, too. For example, from S. Smith, Builders' Detail Sheets, second edition (1991/2009):
Wall plates are not really suitable where joists are supported by an external wall, and in this case a mild steel or wrot iron bar may be used. Fig 3.
The joists may rest on a wall plate supported by wrot iron or MS corbels Fig 4.
And from Metal Statistics, volume 86 (1994):
Melting Steel, Railroad No. 1
Clean wrot iron or steel scrap, 1/4 inch and over in thickness, not over 18 inches in width, and not over 5 feet in length. May include pipe ends and material 1/8 inch to 1/4 inch in thickness, not over 15 inches x 15 inches. Individual pieces cut so as to lie reasonably flat in charging box.
Instances such as these (and the one that the poster asks about) suggest that even if the spelling is generally obsolete, readers may run across it in fairly recent publications. There is little evidence, however, to suggest that wrot is widely used as a variant of wrought in publications today.