What's the deal with the 3.5mm hex screws?
10-24-21, 06:58 AM
#1
Road Runner
Thread Starter
What's the deal with the 3.5mm hex screws?
I needed to replace the disc on one of my bikes, and since the (OEM) Shimano parts aren't available, I picked up one by SRAM. The Shimano had been held on by Torx bolts but the SRAM came with hex socket bolts. So I started inserting the new bolts and quickly found that the socket was neither a 3mm or 4mm, but instead apparently 3.5mm! Most of my sets and multitools include a 2.5mm key, but I have never seen or heard of a 3.5. Fortunately -- as always -- I found one on Amazon for about $5 and it should be here later today so I can finish the job. I've never done much with disc brake maintenance, but has this sizing become common on newer bikes? Can 3.5mm fasteners be found elsewhere?
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10-24-21, 08:55 AM
#3
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SRAM are T25 as well. If it's a problem just reuse the old fasteners.
10-24-21, 10:37 AM
#4
Road Runner
Thread Starter
Thanks. This is embarrassing -- the problem is with my eyesight! It's indeed a T25, but they have a gloss black finish and I couldn't distinguish the star shape so thought is was a standard hex of an unusual size.
I was planning on an appointment with my ophthalmologist and new glasses -- guess I'll up the priority on that.
I was planning on an appointment with my ophthalmologist and new glasses -- guess I'll up the priority on that.
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10-24-21, 03:30 PM
#5
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I feel your pain.
I have look more carefully for a longer time to decide if some of the smaller socketed screws I have to loosen or tighten are torx or hex. Especially since I've misplaced the loupe magnifier I use to keep in my pocket.
I have look more carefully for a longer time to decide if some of the smaller socketed screws I have to loosen or tighten are torx or hex. Especially since I've misplaced the loupe magnifier I use to keep in my pocket.
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10-25-21, 09:35 AM
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Don't feel bad. I made the same mistake 
on a bleed port on my fat bike brakes due to the same glossy black finish you are talking about. The hex wrench wasn't fitting right, and luckily I decided to just see if a T25 would work. Very hard to see sometimes.
on a bleed port on my fat bike brakes due to the same glossy black finish you are talking about. The hex wrench wasn't fitting right, and luckily I decided to just see if a T25 would work. Very hard to see sometimes.
