"What has three feet, but can't…

A yardstick riddle is:

Q: What has three feet, but can’t walk?
A: A yardstick.

The riddle has been cited in print since at least 1899.

Newspapers.com
26 August 1899, The Champaign County News (Champaign, NY), pg. 7, col. 5:
Conundrums Answered.
What has three feet but can’t walk? A yardstick.

Newspapers.com
17 June 1921, The Gazette and Daily (York, PA), “Riddles Sent in By Members of Birthday Club,” pg. 14, col. 3:
Margaret Spahr, Dover.
What has three feet and cannot walk? Ans.—A yard stick.

Newspapers.com
28 November 1921, The Gazette and Daily (York, PA), pg. 4, col. 6:
What has three feet and can’t walk? Ans.—A yard stick.

Google Books
Almanac
The Louisiana State Board of Health
1926
Pg. 13:
What has three feet and cannot walk? A Yard Stick.

Newspapers.com
11 June 1933, The Sunday Star (Indianapolis, IN), magazine sec., pg. ?, col. 6:
What has three feet but can’t walk?—Sophie Estelle Dugoleski.
(...)
A yardstick.

Newspapers.com
23 July 1938, The Herald (Miami, FL), “Uncle Ray’s Corner,” pg. 3B:, cols. 1-2:
What has three feet but can’t walk?
(...)
A yard stick.

Google Books
Practical Classroom Procedures for Enriching Arithmetic
By Herbert F. Spitzer
St. Louis, MO: Western Publishing Co.
1956
Pg. 60:
What has three feet and can’t walk?
ANSWER: A yardstick.

Google Books
The Giant Book of Family Fun and Games
By Jack Tedford
New York, NY: F. Watts
1958
Pg. 100:
What has three feet but cannot walk?
A yardstick.

Google Books
Arithmeriddles
By Lowry Waring Harding
Columbus, OH: Association for the Study of Educology, Ohio State University
1961
Pg. 44:
Q. What is there about a yardstick that is especially noteworthy?
A. It has 3 feet but cannot walk.

Google Books
September 1962, Boys’ Life, “Think and Grin,” pg. 86, col. 2:
Jim: What has three feet and can’t walk?
Tim: A yardstick. — Benny Cousar, Jr., Washington 1, D.C.

Newspapers.com
17 February 1973, Enquirer and News (Battle Creek, MI), The Mini Page sec., pg. 3, col. 1:
Q. What’s long, has 3 feet, but cannot walk?
A. A yardstick.
—Bobby Heath, Coldwater.

Newspapers.com
9 September 1973, Fort Worth (TX) Star-Telegram, “Mini Jokes,” The Mini Page, pg. 3, col. 1:
Question: What has 3 feet, can’t walk and can’t talk?
Answer: A yard stick.
—Ann Irwin, 9
Krum

Google Groups: alt.humor.puns
Puns of the Weak: 05-02-03
Stan Kegel
May 5, 2003, 3:59:23 AM
(...)
Why did the yardstick have trouble buying shoes?
Because it has three feet (Daiy Groaner)

Twitter
CHANEL
@_chanelsade_
RT: @__lalalalydia What has three feet but can’t walk? <=...a yardstick.

1:58 AM · Sep 23, 2010·Twitter Web Client

Twitter
michael nguyen
@MiKEEOHHHH
Ryan: what has 3 feet but can’t walk?
Me: a yardstick?
Ryan: wow don’t tell me u have those popsicle sticks too
LOLLL
9:28 PM · Nov 8, 2010·Twitter SMS

Twitter
coolshades
@cool_shades
Today’s lame popsicle stick joke: What has three feet but can’t walk? A yardstick
5:06 PM · Dec 26, 2010·Twitter Web Client

Twitter
domino
@W__Domino
Popsicle joke #2: WHAT HAS THREE FEET AND CANT WALK?............A YARDSTICK…....y am I even wasting my time? Lol
1:52 AM · Aug 1, 2012·Twitter Web Client

Twitter
Jeannie
@Star_enilnO
Q: What has three feet but cannot walk?
A yardstick #VOTERENDON
1:16 PM · Jul 6, 2017·Twitter for iPhone

Google Books
Reader’s Digest Fun Jokes for Funny Kids Vol. 2
Edited by Reader’s Digest
New York, NY: Studio Fun International
2019
Pg. ?:
Q: What has 3 feet but cannot walk?
A: A yardstick.

Twitter
Jimmy RevJim Olsen
@mybuddyjimmy
What has 3 feet but cannot walk? Yardstick. #RiddleoftheDay
3:22 PM · May 9, 2021 from Des Moines, IA·Twitter for iPhone

“What has three feet, but can’t walk?”/“A yardstick.”