properties /measurement

How far the thread runs from the seat to the end of the shell, as a length. NGK publishes it as its own catalogue column, headed "Thread length (Reach)", with the values 9.5, 11.2, 12.7, 17.5, 19.0 and 26.5 mm across its shell codes; Bosch's designation table publishes the same figures (`A 12.7`, `D 19`, `E 9.5`, `M 26.5`, with 11.2, 17.5 and 25 as the matching half-thread lengths); Champion prints `Reach 0.75 in` for the RN9YC. IT IS INDEPENDENT OF THE THREAD [A11]: Denso's SK20R11 and SK20HR11 carry the same M14 x 1.25 joint and differ only here, 19.0 mm against 26.5 mm — two separate part numbers, two separate boxes, one number apart. A plug with too much reach meets the piston; one with too little leaves hot thread exposed in the chamber, so this is the fact a counter clerk actually has to get right. (It is also, and only incidentally, what Habib's shelf has been saying all along in Swahili — *Pini Fupi* short pin, *Pini Ndefu* long pin — but the differentia stands on NGK's and Bosch's published tables, not on the shop's nickname [L12].) Distinct from the spine's `length`, which is a whole product's overall extent: a plug's overall length includes the insulator and the terminal and is not what any catalogue means by reach.