"Cobble" defined

A cobble (sometimes a cobblestone) is a clast of rock defined on the Udden–Wentworth scale [below] as having a particle size of 64–256 millimeters (2.5–10.1 in), larger than a pebble and smaller than a boulder. Other scales define a cobble's size in slightly different terms. A rock made predominantly of cobbles is termed a conglomerate.

φ scale	Size range (metric)	Size range (approx. inches)	Aggregate name (Wentworth class)	Other names
<−8	>256 mm	>10.1 in	Boulder
−6 to −8	64–256 mm	2.5–10.1 in	Cobble
−5 to −6	32–64 mm	1.26–2.5 in	Very coarse gravel	Pebble
−4 to −5	16–32 mm	0.63–1.26 in	Coarse gravel	Pebble
−3 to −4	8–16 mm	0.31–0.63 in	Medium gravel	Pebble
−2 to −3	4–8 mm	0.157–0.31 in	Fine gravel	Pebble
−1 to −2	2–4 mm	0.079–0.157 in	Very fine gravel	Granule
0 to −1	1–2 mm	0.039–0.079 in	Very coarse sand
1 to 0	0.5–1 mm	0.020–0.039 in	Coarse sand
2 to 1	0.25–0.5 mm	0.010–0.020 in	Medium sand
3 to 2	125–250 µm	0.0049–0.010 in	Fine sand
4 to 3	62.5–125 µm	0.0025–0.0049 in	Very fine sand
8 to 4	3.9–62.5 µm	0.00015–0.0025 in	Silt	Mud
10 to 8	0.98–3.9 µm	3.8×10−5–0.00015 in	Clay	Mud
20 to 10	0.95–977 nm	3.8×10−8–3.8×10−5 in	Colloid	Mud

I looked this up because something I read caused me to wonder whether the word "cobbler" and the phrase "cobble something together" were related to cobblestones.  The answer (from the more-convenient-than-the-OED Online Etymology Dictionary) seems to be "maybe."

cobbler (n.1)

late 13c., cobelere "one who mends shoes," of uncertain origin. It and cobble (v.) "evidently go together etymologically" [OED], but the historical record presents some difficulties. "The cobbler should stick to his last" (ne sutor ultra crepidam) is from the anecdote of Greek painter Apelles.

cobble (v.)

"to mend clumsily," late 15c., perhaps a back-formation from cobbler (n.1), or from cob, via a notion of lumps.

cobbler (n.2)

"deep-dish fruit pie," 1859, American English, perhaps related to 14c. cobeler "wooden bowl."

cob (n.)

a word or set of identical words with a wide range of meanings, many seeming to derive from notions of "heap, lump, rounded object," also "head" and its metaphoric extensions. With cognates in other Germanic languages; of uncertain origin and development. "The N.E.D. recognizes eight nouns cob, with numerous sub-groups. Like other monosyllables common in the dial[ect] its hist[ory] is inextricable" [Weekley]. In the 2nd print edition, the number stands at 11. Some senses are probably from Old English copp "top, head," others probably from Old Norse kubbi or Low German, all perhaps from a Proto-Germanic base *kubb- "something rounded." Among the earliest attested English senses are "headman, chief," and "male swan," both early 15c., but the surname Cobb (1066) suggests Old English used a form of the word as a nickname for "big, leading man." The "corn shoot" sense is attested by 1680s.