“Not worth a tinker’s dam” (“Not worth a tinker’s damn”)

“Not worth a tinker’s damn” refers to the swearing of tinkers (common laborers who were known to swear often in the early 1800s). The expression means that something is insignificant or worthless.
 
“Tinker’s curse” has been cited in print since at least 1813. “Not worth a tinker’s .. blessing!” was printed in an 1817 newspaper. “Not worth (to use expression excited by honest indignation) a tinker’s damn” was printed in Rambler’s Magazine on May 1, 1823.
 
“Tinker’s dam”—with an explanation in support of this spelling—was printed in the Hartford (CT) Daily Courant on November 19, 1856. However, given the history of the term, “tinker’s dam” is not a spelling that correctly reflects the term’s meaning, although this spelling is frequently used.
 
   
WIktionary: Tinker’s damn
Etymology
Merriam-Webster finds tinker’s damn in print since 1839 and suggests that it derives from tinkers’ reputation for swearing. The spelling tinker’s dam is attested since 1858, and phrases.org.uk notes the disagreement over whether the term originated from tinkers’ swearing or instead from their use of small, single-use dams to hold solder. The latter explanation has been offered since 1877; on the other hand, the phrase tinker’s curse is attested since 1824 and the phrase worth a tinker’s cuss is attested since 1854, for which reason Etymonline considers the “dam” derivation an “ingeniously elaborate but baseless” invention of later writers.
Noun
tinker’s damn
1. An insignificant or worthless amount or thing.
     
Merriam-Webster
tinker’s damn noun
variants: or less commonly tinker’s dam
Definition of tinker’s damn
: a minimum amount or degree (as of care)
First Known Use of tinker’s damn
1839, in the meaning defined above
History and Etymology for tinker’s damn
probably from the tinkers’ reputation for blasphemy
 
(Oxford English Dictionary)
tinker, n.
not to care, be worth, (etc.), a tinker’s curse, cuss, or damn, (ellipt.) a tinker’s, an intensification of the earlier ‘not to care, or be worth, a curse or damn’ (see curse n. 2   ⁋, damn n. 2), with reference to the reputed addiction of tinkers to profane swearing: see 1. Cf. also quot. 1884, in which ‘not to care a straw’ is similarly intensified. (An ingenious but baseless conjecture suggesting another origin appears in quot. 1877.)
[1824   J. Mactaggart Sc. Gallovidian Encycl. v. Sir Balderdash at Balderdash   A tinkler’s curse she did na care What she did think or say.]
1839   H. D. Thoreau Jrnl. 25 Apr. (1981) I. 72   ‘Tis true they are not worth a ‘tinker’s damn’.
1862   C. F. Browne Artemus Ward his Bk. 155   Not keerin a tinker’s cuss.
[1877   E. H. Knight Pract. Dict. Mech.  Tinker’s-dam, a wall of dough raised around a place which a plumber desires to flood with a coat of solder. The material can be but once used; being consequently thrown away as worthless, it has passed into a proverb, usually involving the wrong spelling of the otherwise innocent word ‘dam’.]
1884   St. James’s Gaz. 24 Apr. 12/1   I don’t care two tinkers’ straws if you do.
1891   R. Kipling Light that Failed vii. 137   The real world doesn’t care a tinker’s—doesn’t care a bit.
     
Google Books
The History and Adventures of Godfrey Ranger,
Vol. II
By David William Paynter
Manchester, UK: Printed and Sold by R. & W. Dean
1813
Pg. 143:
“Will they, by G—!” cried a sixth, “then they a’n't worth a pedlar’s curse!” “You mean a tinker’s curse, friend!” shouted a seventh.
 
18 April 1817, Western Herald & Steubenville Gazette (Steubenville, OH), pg. 2, col. 4:
Owl Creek. Not worth a tinker’s .. blessing!
     
Google Books
1 May 1823, Rambler’s Magazine, pg. 216:
... not worth (to use expression excited by honest indignation) a tinker’s damn and if Mrs. Chatterly has no other salvo for her precious reputation than the word of Christmas, she had better, in future, act upon her professional character alone, ...
 
Newspapers.com
14 December 1833, The Times (London, UK), “Police,” pg. 6, col. 4:
One of the paupers said, “Please you, my Lord, the beer is very queer, for Mr. Waddington gives it so heavy a dash of Adam’s ale that, saving your presence, it isn’t worth a tinker’s d—n.”
   
Newspapers.com
21 September 1834, The Observer (London, UK), “Sir Charles Flower, Bart,” pg. 2, col. 5:
The Alderman looked at him with awe, for he “canted” into his plate the green dollops, leaving to his brethren the forced meats and fluid, and those other parts of the delicacy which he considered not worth a “tinker’s damn.”
 
15 January 1836, Barre (MA) Gazette, pg. 1, col. 5:
New Year’s Addresses. The best we have yet read, and the only one worth a tinker’s blessing is the subjoined presented to us yesterday, ...
 
Chronicling America
16 January 1840, Morning Herald (New York, NY), “Post Office,” pg. 3, col. 1:
Well, the latter turned over the garment, and then she said I was not worth a tinker’s d—.
   
11 June 1842, The Spirit of the Times (New York, NY), “Dublin Police Doings,” pg. 177, col. 2:
Miss Hackett—The witness is Mrs. Dowling’s daughter, an’ her oath isn’t worth a tinker’s curse.
   
Newspapers.com
Chronicling America
4 April 1846, The Spirit of Democracy (Woodsfield, OH), “One Dollar a Week and Found,” pg. 1, col. 2:
Now, of all occupations, in the eyes of old Drayton, that of a tinker was held the most odious and abominable. “Not worth a tinker’s curse,” was his favorite oath—and he uttered it apparently with a fervent appreciation of the utter signification of its import.
 
Newspapers.com
19 November 1856, Hartford (CT) Daily Courant, pg. 2, col. 4:
NOT AS PROFANE AS THEY MEAN TO BE.—In choosing their expletives, persons of loose language are apt to use what they take to be a——peculiar to the professional repairers of pots and pans, who are not reponsible for the wicked phrase attributed to them—as will appear from the following explanation. Tinkers, as trampers, of course carried their own provisions. When called upon for their services, they very naturally masticated a piece of bread and formed therewith a dam to prevent the solder from becoming discursive. The said dam after doing this duty had of course a very marketable value as food, and hence the expressive phrase for comparisons,—“Not worth a tinker’s dam.” Assuming this interpretation to be correct, it will not excuse those who have used the phrase in question, (adding an “n” to the last word,) with an express design of swearing. They meant to be wicked, and sin (preachers say) is the intention. Consequently, if they were not profane, verbally, and in the overt act, they have only their ignorance to thank for their salvation.