This is the 13274th most frequent Russian word.
монтажные
"Монтажные" translates to "assembly" or "installation-related."
In this sentence, 'монтажные' is used as an adjective modifying 'работы' to denote tasks related to installation or assembly.
Мы начали монтажные работы на объекте.
We commenced installation works at the site.
Here, 'монтажные' describes 'инструменты', indicating tools that are related to assembly activities.
У меня есть монтажные инструменты для ремонта.
I have assembly tools for repair.
'Монтажные' in this case modifies 'проекты', referring to designs or plans connected with installation or assembly processes.