The phrase "extension kit" is correct and usable in written English.
It can be used when referring to a set of tools or components designed to extend the functionality of a device or system.
Example: "To enhance the capabilities of your printer, consider purchasing an extension kit that includes additional cartridges and accessories."
Alternatives: "expansion kit" or "add-on kit".
Morphology Extension Kit: A Modular Robotic Platform for Physically Reconfigurable Wearables.
Sang-won Leigh, et al. "Morphology Extension Kit: A Modular Robotic Platform for Physically Reconfigurable Wearables". TEI 18, pp 11-18, March 3 , 2018
AASM comprises a frontal guidance kit and a rear-mounted range extension kit matched to a dumb bomb.
The current model features a 250 kg bomb matched to a nose-mounted guidance kit and a rear-mounted range extension kit, containing a rocket booster and enlarged fins.
When no differential restriction maps were available, the ABI Prism SNaPshot ddNTP Primer Extension Kit (Applied Biosystems) was used for SNP genotyping [ 23].
These probes were labeled by random primer extension kit (Rediprime II DNA Labelling System, Amersham Biosciences, Inc., Piscataway, NJ) with 50 µCi of [α-P]dCTP.
Various online gun outlets in Australia offer cheap and easy extension kits that would allow a person to legally import a firearm and then extend its magazine's capacity.
Mr. Kuznetsov's company here, Belli Capelli, which processes human hair into extension kits, is the largest business of its type in Russia, with annual revenue of about $16 million.
The starter kit will cost around $40. Two extension kits (with two more casting molds each) will be available at the same time (price: $18 each).
If the walk-in tub doesn't quite fit your old bathtub space, extension kits are available to ensure a good fit.
Primer extension kits are commercially available from Promega Corporation.
