You can find a LinkedIn group for almost any engineering topic. The trick is to find groups that are active with a lot of ongoing discussions. Some of the groups we found are for members only, but becoming a member is usually as easy as sending a request to the administrator.

Mechanical Design Engineering
This members-only group is open for professionals, students, recruiters, and others in mechanical engineering who are interested in mechanical-design subjects. It is listed as very active with 746 discussions the month we checked and 9,544 members.

Engineering Career Opportunities (Jobs & Employment)
This members-only group serves the engineering and recruiting communities by letting employers connect with job seekers. It is ranked as very active with 2,133 discussions the month we checked in and 74,260 members.

Reverse Engineering, Mechanical and Electrical
This group specializes in the lean way of product development and is ranked very active with 57 discussions recently and 2,052 members.

ASME (American Society of Mechanical Engineers)
The ASME group is also members only and ranked as very active with 331 discussions the month we checked and 63,098 members.

Mechanical Design Forum
This members-only group discusses technical mechanical engineering subjects in industrial and manufacturing and product design, and bills itself as not run by recruiters. It had 67 discussions the month we checked and 27,027 members.

Mechanical Engineer Jobs
This members-only group primarily focuses on mechanical engineering, jobs, job outlooks, and advice from mechanical engineers to mechanical engineers. It had 352 discussions in a recent month and 20,000 members.

Mechanical Engineers Network
This group appeals to engineers looking for opportunities to network with other like-minded engineers, engineering-based companies, or recruiters. It recently hosted 257 active discussions and 20,000 members.

Mechanical Engineer Forum
Another members-only group of mechanical engineers for discussing the engineering world and to receive advice from other mechanical engineers. It is active with 24 recent discussions and 8,650 members.

The Engineering Forum
This group is billed as a place where structural, mechanical, civil, wastewater, and design engineers can share ideas about career goals and jobs. There are 3,596 recent discussions and 7,622 members.

Engineering Jobs in USA and Canada
This group is for all kinds of professionals in engineering. In the month we checked, it hosted 342 discussions and 3,647 members.

Freelance Design Engineering
This is a members-only group for engineers looking at doing freelance or contract work in mechanical, electrical, public health, design, and various other areas. There were 66 discussions the month we checked and 3,153 members.

Bicycle design and engineering
This members-only group aims to bring together people who are impassioned by designing and/or engineering bicycles. It recently hosted 69 discussions and 2,179 members.

Electrical Engineering
This is a members-only group that is basically for all electrical engineers worldwide and is very active, with 240 recent discussions and 14,736 members.

Electrical Engineer
Another members-only group for EEs that is very active: Two-hundred eighty-one recent discussions and 19,945 members.

Electrical Engineers Online
This members-only group for EEs hosts articles of interest to EEs as well as news from the field, with 58 recent discussions and 2,986 members.

Automation & Control Engineering
A group designed to share information, insights, and opinions on industrial automation and control in discrete manufacturing and process industries. Sixty-five recent discussions and 36,071 members.

Automation Engineers
Another big group designed for people within the automation industry to stay in touch and share information. Very active with 199 recent discussions and 26,936 members.

Automation
Automation.com created this group to let industrial-automation, process-control, and instrumentation professionals network. Twenty-five recent discussions and 23,726 members.

Industrial Automation and Controls Network
This is a members-only technical networking group for people in industrial automation and process controls. One-hundred seventeen recent discussions and 12,012 members.

Factory Automation
This one is billed as a gathering site for people having interest in factory automation. Thirty-one recent discussions and 690 members.