Hamilton 980, 986, 987, 987A, 979 mainsprings

Hi ,
I have searched the Hamilton data books and came away more confused than when I started. (Not an unusual state for me).
I also looked in the Bestfit book 111 with no more success.
Dose anyone know what sizes (Dennison or Metric) goes with each movement.
It looks like the same mainspring goes with more than one movement.
Also does it matter if it is white alloy or blue steel.
Thanks in advance.
Mel
PS these are 14/o, and 6/o sizes.

Hello Melvin,

Mainsprings are as follows;

Grade 980 Mainspring Part#5021
Dennison 4-10-11 1/2

Grade 986 Mainspring Part#1921
Dennison 5-8 1/2-10

Grade 987 Mainspring Part#2521
Dennison 5-9 1/2-11 1/2

Grade 987A Mainspring Part#2321
Dennison 4-9 1/4-11 1/2

Grade 979 Mainspring Part#2621
Dennison 5-10-11 1/2

Erin (Bila's Daughter)

Many , many thanks for the info.
Mel

Hi and Thanks again.
Just rechecking for the 987A mainspring
You have it as 4-9 1/4-11 1/2

I have seen it as 4 1/2-9 1/4- 11 1/2
Any chance both were used???
Mel

Hi Melvin,

I to have seen 4 1/2, 4 3/4 and also 5 in heights on both Hamilton and other Brand Manufacturer's mainspring packets for this spring number. To my and Dad's knowledge the figures are very mis-leading in most circumstances,why? This comment and some of the following overview can apply to other size Watches and their mainsprings as well

I say this because if you take say the Hamilton genuine mainspring marked as "Dennison 5" from a packet and measure it, the reading you will get in metric is 1.32-1.34mm. To my knowledge "Dennison 5" is actually the equivalent of 1.40mm.

This also applies to Manufacturer's like "Security, Tri-Time, HR, Marco (Marshall Brand) and Hamilton as I said above and others. Some of these Brands list Dennison 5 on their packets with a degree of varying sizes below the number 5 in metric ranging from 1.35,1,37 through to 1.40mm, so it looks like different Manufacturers had a different take on what Dennison 5 actual was.

Now if you look at the mainspring barrel and measure it correctly on a 987A from just after World War 2 you will see usable height as 1.43mm, but you must allow clearance for thrust forces (end-float). To Dad's knowledge you should have about .1mm or 4 thou clearance between the top & bottom of the barrel so that means a spring of no more then 1.33-1.34 in width.

This is why I think in Hamilton's Part's catalogue from just after the war specify a "Dennison 4 spring" which is the equivalent of 1.30mm. Although to confuse matters more Melvin if you look at Hamilton's own parts catalogue from the 1960's they specify Dennison 5 mainsprings for all 6/0's watches. So to cut a very long story short as long as the Mainspring is under the 1.33-1.34mm in height it will be fine.

I suppose the moral of the story is before sending out or using a mainspring it is always best to measure the spring before using it I am afraid to say. My apologies for such a long winded post but Dad was adamant that I highlight all of the reasons

Hi Erin,
On the contrary I appreciate the dialogue.
The whole thing started as I was (am) confused by the lack of specificity when going to dimensions for lots of parts, staffs stems mainsprings etc.
Was hoping the labels on the parts I have were wrong, but I see that many different sizes are designated for the same movement.
Thanks again.
Mel