Pianotech

I will be working on a repair of a pinblock that has separated from the back of a spinet. I can't find my notes from the last time I did this repair and was hoping that someone could help me with the correct size of carriage bolt to buy. I specifically need the diameter that will replace the place screws. The length should be about 7-8 inches. Because this will be done at a customers home, I will not have the luxury of getting the bolts after taking the screws out.

Thank you.

------------------------------
Rex Roseman
Roseman Piano Tuning
Copley, OH
330-289-2948
------------------------------

Rex,

5/16" bolts is what I've always used on these. Sometimes flathead, sometimes hex depending on what was used where. This assumes putting them through from the front. Sounds like you want to put them through from back, thus the carriage bolt style with the squared part under the head. Either way works. 

Peter Grey Piano Doctor 

------------------------------
Peter Grey
Stratham NH
(603) 686-2395
pianodoctor57@gmail.com
------------------------------

Please don't leave like this.

------------------------------
Larry Messerly, RPT
Bringing Harmony to Homes
www.lacrossepianotuning.com
ljmesserly@gmail.com
928-899-7292
------------------------------

Original Message:
Sent: 10-01-2026 20:33
From: Peter Grey
Subject: Pinblock/Back separation repair

Rex,

5/16" bolts is what I've always used on these. Sometimes flathead, sometimes hex depending on what was used where. This assumes putting them through from the front. Sounds like you want to put them through from back, thus the carriage bolt style with the squared part under the head. Either way works. 

Peter Grey Piano Doctor 

------------------------------
Peter Grey
Stratham NH
(603) 686-2395
pianodoctor57@gmail.com
------------------------------

Original Message:
Sent: 10/1/2026 9:05:00 PM
From: Larry Messerly
Subject: RE: Pinblock/Back separation repair

Please don't leave like this.

------------------------------
Larry Messerly, RPT
Bringing Harmony to Homes
www.lacrossepianotuning.com
ljmesserly@gmail.com
928-899-7292
------------------------------

I would use the largest grade 8 bolts that will fit and an epoxy with a long working time.

------------------------------
Parker Leigh RPT
Winchester VA
(540) 722-3865
------------------------------

3/8" might work too depending on what's already in there, that might be overkill, plus you'd need a long drill bit, plus grade 8 is somewhat overkill too.  Ive never had a 5/16" bolt fail under this or any other condition. Its not a boiler on a submarine... 😉 

Peter Grey Piano Doctor 

------------------------------
Peter Grey
Stratham NH
(603) 686-2395
pianodoctor57@gmail.com
------------------------------

Original Message:
Sent: 10-02-2026 20:17
From: Parker Leigh
Subject: Pinblock/Back separation repair

I would use the largest grade 8 bolts that will fit and an epoxy with a long working time.

------------------------------
Parker Leigh RPT
Winchester VA
(540) 722-3865
------------------------------

I've done dozens of split pinblock repairs. Most were done with heat-treated threaded rod cut to length onsite with nuts on either end. That way they don't have to be overlong, and I didn't have to worry about having the right size, or the proximity to the nearest hardware store. All were done with standard wood glue. 

Spinets are problematic because there is often little to no space for a bolt above the tuning pins. A friend advised me, if you can't go for quality, go for quantity. On one, I chose to use a couple dozen wood screws aimed in between tuning pins. Held fine. 

------------------------------
David Stocker, RPT
Olympia WA
------------------------------

David,

Yes, and this is why I also use (where needed) a flat head bolt inserted from the front and a recessed nut from the rear. Excess bolt length gets cut off. 

Between the sandwich bolts and whatever adhesive one puts in there, it ain't comin apart anytime soon. Interesting how '50s Steinways seem to have this problem regularly (then again it simply reinforces the fact of the "design lifespan" of all of these products).

Peter Grey Piano Doctor 

------------------------------
Peter Grey
Stratham NH
(603) 686-2395
pianodoctor57@gmail.com
------------------------------

Original Message:
Sent: 10-04-2026 00:42
From: David Stocker
Subject: Pinblock/Back separation repair

I've done dozens of split pinblock repairs. Most were done with heat-treated threaded rod cut to length onsite with nuts on either end. That way they don't have to be overlong, and I didn't have to worry about having the right size, or the proximity to the nearest hardware store. All were done with standard wood glue. 

Spinets are problematic because there is often little to no space for a bolt above the tuning pins. A friend advised me, if you can't go for quality, go for quantity. On one, I chose to use a couple dozen wood screws aimed in between tuning pins. Held fine. 

------------------------------
David Stocker, RPT
Olympia WA
------------------------------