4.8(1,922)Amazon rating$26.99200+ bought last month
Our verdict
The Klein 646M is a 9.75-inch hollow-shaft nut driver with a 6-inch fastener capacity weighing 0.42 pounds, priced at $26.99 and backed by a 4.8-star rating from 1,922 reviews and 200 buyers last month.
Electricians and HVAC technicians who regularly drive long fasteners or work with conduit knockouts requiring hollow-shaft clearance.
Skip if
Buyers who only need a compact driver for short fasteners or those who are not willing to spend $26.99 on a single nut driver.
Length 9.75 Inches
Weight 0.42 Pounds
Capacity 6 Inches
Priced 69% above the category median ($15.99 across 47 tracked models)
Our scorecard
4.8/5overall
Owner rating4.8/5
4.8 average across 1,922 owner ratings
Popularity4.1/5
1,922 owner reviews, more than most models here
The overall score is owner satisfaction weighted by how many reviews back it, so a high rating from few reviews counts for less. The bars below show where this model stands against the other hand tools and workshop hand tools we track in this category on price, popularity and size. Context, not marks against it, and our read of the data, not a lab test.
Overview
The Klein 646M is a standout nut driver by the numbers: 1,922 reviews at 4.8 stars and 200 buyers last month put it among the most validated and actively purchased tools in the nut driver segment. The 9.75-inch overall length and 6-inch hollow-shaft capacity make it purpose-built for long-reach applications where a solid-shaft driver simply cannot reach the nut.
At 0.42 pounds, the 646M is heavier than compact nut drivers but manageable for a full-length hollow-shaft tool. The 9.75-inch length gives leverage for difficult fasteners while the hollow shaft accommodates conduit studs, long bolts, and machine screws that extend well beyond the nut head. At $26.99, it sits in the mid-premium tier for single nut drivers.
For electrical and HVAC work where hollow-shaft access is a daily necessity, the Klein 646M is the most proven option in the data set by review volume and buyer frequency. The combination of length, capacity, and sustained demand from professionals makes a strong case for it.
Pros
4.8-star rating from 1,922 reviews is the strongest review signal in this segment
200 buyers per month reflects active and consistent professional demand
9.75-inch length provides excellent reach and leverage for difficult fasteners
6-inch hollow-shaft capacity handles long fasteners that solid-shaft drivers cannot
0.42-pound weight is reasonable for a full-length hollow-shaft driver
Cons
At $26.99 for a single driver, cost may be prohibitive for occasional users
9.75-inch length is too long for tight or confined workspaces
Drive size is not published in the listing
Specifications
Length
9.75 Inches
Weight
0.42 Pounds
Capacity
6 Inches
Performance notes
At 9.75 inches long with a 6-inch hollow-shaft capacity and 0.42 pounds of weight, the Klein 646M is engineered for deep-reach nut driving in electrical and HVAC contexts. The long shaft provides torque leverage on stubborn fasteners while the hollow bore prevents the shaft from bottoming out on threaded rods or studs. The 4.8-star average from nearly 2,000 reviews confirms the design works well under real professional conditions.
What buyers say
Owners overwhelmingly praise the Klein 646M for its hollow-shaft design and reach. Professional electricians and HVAC technicians cite it as a daily-carry essential. The sustained 200 monthly buyers indicate this is not a novelty purchase but a repeat buy in trade tool kits.
The drive size is not published in the listing. The model number 646M is associated with Klein's hollow-shaft nut driver series, and buyers should confirm the specific size on the product page.
Can the Klein 646M reach through long threaded rods?
Yes, based on specs the 646M has a hollow shaft with 6 inches of capacity, which allows the shaft to slide over long threaded fasteners or studs without bottoming out.
How does the Klein 646M compare to shorter nut drivers?
The 646M is 9.75 inches long with a 6-inch hollow capacity, making it significantly longer than compact single-piece drivers. It trades portability for deep-reach access in professional trade applications.
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