I do not know what exactly you are trying to do but there is a lot of work done on grip strength.  In a quick search it looks like the standard tool for measuring this is a Jamar dynamometer.

Jamaica 

Hi,

you could maybe find interest in these two papers using a new handgrip ergometer.

sincerely,

Laurent

Characterisation of forces exerted by the entire hand during the power grip: effect of the handle diameter.

https://www.researchgate.net/publication/223987680_Characterisation_of_forces_exerted_by_the_entire_hand_during_the_power_grip_effect_of_the_handle_diameter?ev=prf_pub

Finger force sharing during an adapted power grip task

https://www.researchgate.net/publication/51693294_Finger_force_sharing_during_an_adapted_power_grip_task?ev=prf_pub

Article Characterisation of forces exerted by the entire hand during...

Article Finger force sharing during an adapted power grip task

Strength Measurements of the Intrinsic Hand Muscles: A Review of the Development and Evaluation of the Rotterdam Intrinsic Hand Myometer

by Schreuders, Ton A.R; Selles, Ruud W; Roebroeck, Marij E; Stam, Henk J

Journal of Hand Therapy 2006, Volume 19, Issue 4

Measuring Extrinsic and Intrinsic Hand Strength in Healthy Adults: Inter-Rater Reliability of the Rotterdam Intrinsic Hand Myometer

by Corey McGee; Elizabeth Garlough; Julia Gilbert; Amanda Overlie; Karleen Smurawa

Journal of Hand Therapy, 07/2014, Volume 27, Issue 3

Jamar hand dynamometer (Hydraulic Hand Dynamometer, 5030J1, Sammons Preston, Bolingbrook, IL, USA). This is the adress

And here are presented normal values

Bohannon, R.W., et al., Reference values for adult grip strength measured with a Jamar dynamometer: a descriptive meta-analysis. Physiotherapy, 2006. 92: p. 11-15