Reporting back on this issue; I was able to fix the threads with helicoils.  It 
turned out to be a really easy job.  I locally bought a kit with ¼-20 helicoils 
and the tap and threading tool, drilled the holes out, tapped and threaded in 
the helicoils.  I found that they did not feel that tight when screwed in, so 
added some loctite to the outside before putting them in.  Then I used tef-gel 
on the screw threads.  If I had to do this again, I think I would use the 
threaded inserts that come with outer loctite 
(https://www.amazon.com/dp/B002QUZNV8/ref=emc_b_5_t), but the helicoils seem 
fine for now.  A valuable lesson learned on how to repair bad threads.  Thanks 
to the group for pointing me in the right direction.  Dave

S/V Aries
1990 C&C 34+
New London, CT



> On May 14, 2020, at 10:35 PM, Nathan Post via CnC-List 
> <cnc-list@cnc-list.com> wrote:
> 
> Yes, you drill the hole bigger and tap for the threads on the outside of the 
> helicoil or thread insert.  The other main advantage of using one of these 
> over just tapping for a larger bolt is in softer base materials (aluminum, 
> plastic) it will distribute the screw load and prevent it from stripping in 
> the first place, at least to a point or damaging the threads when the screw 
> is removed and reinserted.  This is especially important if the screw is one 
> that will be installed and removed every year.  I think that there might also 
> be an advantage in preventing a stainless steel screw from seizing/corroding 
> as it will tend to do over time in tapped aluminum, at least in a salt water 
> environment.  For that reason, I would tend toward using a solid insert such 
> as https://www.mcmaster.com/catalog/126/3505 
> <https://www.mcmaster.com/catalog/126/3505> rather than a helicoil if putting 
> a stainless steel screw into threaded aluminum where I want to be sure I can 
> get them apart again.  We had bolt together reusable aluminum frames at my 
> last job with M16 and M24 bolts and used inserts for threaded holes in the 
> aluminum - worked great and we never had issues with stripping or galling of 
> the threads.
> 
> ~~~
> Nathan Post
> S/V Wisper
> 
> 
> On Thu, May 14, 2020 at 10:18 PM Graham Collins via CnC-List 
> <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> wrote:
> Hi David
> 
> Yes, allows the use of the original screw, so whatever is fastening to it 
> doesn't have to be modified.
> 
> Procedure is to drill and tap oversized, and install a helicoil - essentially 
> a coil of square wire, wound up like a spring.  The wire engages in the new 
> threads and is sized so that the original screw threads inside it.
> 
> Graham Collins
> Secret Plans
> C&C 35-III #11
> On 2020-05-14 10:50 p.m., David Knecht via CnC-List wrote:
>> I have seen mention of helicoils several times on this list but I have no 
>> experience with them.  I have several stripped screws on my Harken furler 
>> and was thinking they might be useful to repair.  What is unclear to me from 
>> what I have read is the reason to use them.  I still have threads there, and 
>> I thought the idea was to screw in a helicoil to make the threads grab 
>> again.  However, every description I have seen of using them drills out the 
>> hole, taps and then screws in a helicoil.  I don’t get the point.  If I am 
>> going to drill and tap, why would I use a helicoil instead of just putting a 
>> screw into the newly tapped hole?  Is it that you can use the same size 
>> screw as before instead of going to a larger size?  Is that preferable for 
>> some reason?  Dave
>>   
>> David Knecht
>> S/V Aries
>> 1990 C&C 34+
>> New London, CT
>> 
>> 
>> 
>> 
>> 
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